Best Way To Remove Fajita Contents From Marinade

You might be able to counter-balance it with other flavors (salt, sour, sweet, hot), but you're likely still going to have some bitter notes come through, it's just a question if it's tolerable or not, and some people dislike bitter more than others. (I can't understand how people can drink beers other than lambics)

In looking at a similar thread on Chowhound, one of the recommendations is a bit of milk or cream. If you're not lactose intollerant, it might be worth a try.

This could also be a chance for an experiment -- ladle it into a bunch of glasses, try some different things (sugar, vinegar, soy, hot sauce, milk, worcestershire, combinations of them, etc), and report back to us with what you think worked best.

To answer part 1. I recently watched the Chicken Tikka Masala episode from Blumethals "Further Adventures in Search of Perfection". The recipe calls for marinading the chicken for quite a long time. A transcribed recipe says 10 hours: http://www.dominicsayers.com/documents/ChickenTikkaMasala.pdf.

They also go on to compare the results of a yogurt marinade and a yogurt-less marinade on chicken under an MRI scanner. I don't know if this is valid, but the yogurt apparently had an effect.