Well, I don't know if what I'm about to post will actually answer your question or not, but here goes.
A while back I sat down and figured up a new spell formula, similar to permanency, but one that would grant the spell as a supernatural ability or an extraordinary ability. The cost and difficult of the formula was astounding, but it seems to work really well.
In the case of a troll's regeneration, the formula works amazingly well. All I need to do is figure out roughly what level spell would grant full regeneration abilities, the spell's parameters, and the formula would tell me how much the spell would cost to research, how much XP the caster would need to spend to apply the spell to the recipient, and how much total cash the recipient would be required to spend. The catch, and this ended up balancing it out really well, was that the ability purchased permanently counted against you in gold pieces, forever counting against your character wealth. This cost method balanced out the character just as easily and effectively as applying a new ECL. Of course, the character has the option of getting it removed as well.
This also opened up a whole new breed of magic items in my games. These new items can sort of considered to be cursed, as once they are put on, they instantly meld into the character, forever binding the magics to them and bestowing a power/powers as a supernatural ability or an extraordinary ability. The items revert to their natural form when the character is slain and they can also be removed. Removing them, however, is expensive and difficult.
So, for me, yes, it's easy to get a troll's regeneration, albeit very very costly. For you, who knows.
