You can't get him back legitimately but you could probably use the CLUA console or shadowkeeper if you're really enamored with him.
Anyways, you could always justify it by creating some storyline about how giving Yoshimo's heart to Ilmater redeemed his soul and you've used a Bhaalspawn power (obviously not one granted by the actual game) to resurrect him. Why not, you can bring anyone else back -- even if they were killed.
For that matter, I've heard of people importing some of the BG1 NPC's into the game because they liked them. It's your game, do what you like.
