You could use something like OldMansBeard's Henchman System but keep in mind that you won't be able to hire more of the campaign's henchs (unless you just copy all their stats when you make your own characters) and those you do import will not be connected with quests or deliver any convos, basically just another NPC that happens to be under your command. Also, I'm guessing that unless you modified each of the 6 modules yourself, they would not just appear in the next one that opens.
Always amazed me how many folk try to change NWN into BG for some reason, but if that is your taste, give it a shot.
Besides, the combat balance, already a pushover in the OC, will be drastically diluted by adding any more allies. Also, your XP rewards will be less on the scale of about 10-15% less per party member attached.
I can remember playing an Ultima-like module once that was very well made and had a whole hoard of hench accompanying my toon, but at transitions not all would always make it. Even after the designer tried manipulating the scripts better, it was never 100% reliable (IIRC it had something to do with how fast each hench approached the transition area following the PC or something like that). That could potentially become an issue trying it with the OC modules. Not sure how they scripted all those.