I've seen nothing that proves this, but it would be one more twist that wouldn't surprise me:
Slave-One = Boba Fett
Solo = our infamous captain, rescuer of princesses
Fett is Han's No. 1 nemesis. He is supposed to be the Clone 'master' [of the line] if he is first, after Jango's death.
Han has many scenes where his primary enemy is a stormtrooper:
Docking Bay 94, his instict to chase them on the Death Star, his scene being tortured on Cloud City (and that capture, with Fett in the scene), the incident with the Bikerscout "Chewie and me'll take care of this."
It could be all ironic when Han tells Ben "No mystical energy field controls my destiny." Ben laughs to that, but I think there's more to it than just "yeah, well look whose ship the Jedi are catching rides with." I thought, hmmm, well Han marries a Jedi princess and has 3 Jedi children with her, but Ben couldn't know that for certain (and it's EU). But Obi-Wan could have known Han was from one clone template or another, and the Clones exist because of the scheming of the Sith, adepts of one side of the Force.
Next, take Han's survival skills: He knows to gut the TaunTaun and survive the frigid Hoth night; he knows how to find the Imperial's sensor blind spots and piggy-back on a StarDestroyer; he knows Imperial pincher movements "We can still outmaneuver them!"; he knows how to deal with Mynocks; he has strong insincts he things is luck, but knows he's inside a giant space slug; he thinks he knows how to hotwire the shield bunker.
Boba Fett is also the consumate survivor. He's made it through the Clone Wars, since a child, without a father (following Jango's death when he was 12). They fit a pattern - like the Joker and Batman, or Sabertoothe and Wolverine.
Finally, lets take the EU into account. Most facts about Han Solo are known from Anne Crispin's great novels (they are the best Star Wars books!) Han was orphaned at age 3 or younger and doesn't remember his real parents. He found a family named Solo on Corellia, and Thracken Sal-Solo does physically resemble Han very closely. They share a Grandfather, Denn Solo, if they are related: Denn and his wife fled a Corellian colony, Denn taking his son, (Han's father), and his wife taking their daughter, Tion (Han's aunt, Thracken's mom) with the women returning back to Corellia.
Han is 29 in A New Hope. Darth Vader (for comparison) is 41.
In The Phantom Menace, it is 3 years before Han is even born.
Darth Vader is 9, making him 12 when Han is born.
Attack of the Clones is 22 years before A New Hope. Darth Vader is of course, Anakin, and 19 years old. Han Solo would be 7 years old in Attack of the Clones (and likely not in the movie by all accounts of spoilers, though not by EasterEggs). However, Palpatine has Crimson Guards, fully masked then, as the Chancellor's Guards. Don't you think they are already Clones? Before he could go ahead with his plans in Episode 2, these warriors had to be tried and tested.
Some EU says it takes Clones 7 years to become close to adults, then some more training beyond that. If Fett is 12 in Episode 2, that will imply he's been trained for 5 years before he loses his mentor. I don't think the Kaminoans will be just starting to create the Clones in Episode 2, I think that the deal with Jango Fett will have been a done-deal since at least 12 years ago (before The Phantom Menace). Perhaps Jango was a slave once, and this was the price of his freedom, but young Boba was the price he charged for his soul. He can't make the deal during the movie, and have young Boba fully trained during the same week (that Episode 2 takes place in during the course of their lives).
So back to Han, if he is 7 years old, his father or 'progenerator' must be older than Jango (at the time of the conception of Han), and therefore, if Denn Solo actually is Han's grandfather, and the EU fits smoothely with even this surprise twist in cannon, Denn is a father of an escaped Clone, maybe from the line of pirates using them as in "Solo the Black" - who might've been the hunter that stalked his 'brother, Denn' causing him and his wife to flee so many years back. So for Han to be a third generation Clone, AND Palpatine to have been involved, it might sound far-fetched, "but not for a Sith!" Palpatine could've (and should've) been exploring cloning that early on, and if "Darth Sidious" was using pirates (Solo the Black) etc, it would really not surprise me as the Trade Federation are little better than pirates, and Shmi Skywalker was taken and sold into slavery by more of the same types. So, it is all possible. Thracken, by the way, would turn out the same as Han, because the Clone genetics would be dominant in their lineage. The only female offspring was a twin, Denn's daughter, Tion.
This is all far-fetched, but I'll conclude with finally saying it could be true, is like Lucas to do something like this to add to the mythology (lost Jedi Twins, a lone warrior outcast, two droids, a Wookiee, and one of the enemy's own - a Clone Warrior, team up to defeat the evil Empire and restore justice in the galaxy).
Now go back and watch the original trilogy and specifically watch Han, and pretend he is a lost Clone. See what happens to him, and you'll see it could fit in and be possible.[/list]