You are correct that Grapefruit interferes with the Cytochrome P450 liver detoxification pathway, but this doesn't seem to affect liver flushing. Although it is a reason why grapefruit shouldn't perhaps be consumed regularly.
First off you shouldn't be taking any medication anyways - certainly not on flush day. Even supplements should not be taken.
So really there is no reason why grapefruit can't be taken. If there was people would have discovered it by now.