Lemon works, I've heard that OJ works, but that might have been in combination with some lemon. Not sure what the juice really does -- just makes the oil palatable? Does anyone know?
Are you sure it's not the OO (Olive-Oil) that's causing the stomach upset? Have you tried just drinking grapefruit juice by itself to see if that's really the cause?
I'm trying safflower oil tonight to see how that goes. I believe it's the OO (Olive-Oil) that's causing bile to come up at night for me.