Really? Your best bet is perhaps a Gestalt "hero" character that serves as your bfs avatar and the parties face... and two loyal "servant" cohort NPCs that are under the control of your BF.
A rogue and a Cloistered Cleric (Info on the Cloistered Cleric can be found here:
Variant Character Classes :: d20srd.org.
Although your BF will be commanding the Rogue and C. Cleric you will be the one leveling them up and playing their personalities/buying equipment and so forth... so if he starts say, ordering them to do crazy ridiculous things you can start having them rebel, threaten to leave, whichever.... even though he's rolling all the dice for them.
He need not "order them" every step of the way, they effectively become PCs when he wants them to do something... i.e. I want Mick the Rogue to scout ahead... and he "becomes" Mick the rogue and rolls for Mick the Rogue... however when Mick the Rogue has enough XP for level 6 you are the one to choose the feats.
You'd be wise to give the Rogue kinda terrible charisma and only bump the CCs fair to Middlin.
Finally, both of these will give you a HUGE amount of plot control.... the Cloistered Cleric can make knowledge checks when you're all 'stumped' and the rogue will help you fine tune dungeon situations.