You can dismiss a character if taken into an isolated map on their own and you run off. You can then return to the main map and the rest of your party, the other half of any partnerships will stay with you - they will not initiate their "I'm staying with so & so" dialogue because the first person never go to talk to you.
"Um... you stay here for a minute Khalid, I just have to have a 'word' with Jaheira in private"
