[Kaleban]

Its quite simple. Start a Multi game. Put in the number of characters you want. Then save the game (manually, not Quick or Auto).

Then go into your HD, open up your BG2 folder and look for the "mpsave" directory. Open that up. There should be a folder with a string of numeric characters before the name you entered for the save. Right-click on it and Copy it.

then open up your "save" folder, and Paste the copied folder into that directory. You can now play your multi game in single-player mode. Only hitch is that the special quests, abilities and dialogue will still be centered around your primary PC, and not any others you bring along.