I have read Micheals sticky on potty training but this topic is not covered. I have Oscar my

"potty trained" to go on his training perch (newspaper below)....he will indicate to me when he has to go and I will bring him over and he does his business. I have been training flight recall and he will go his perch on cue as well. That being said, I am not sure how to bridge the gap in this training. I have thought about recalling him to his perch when I know it is time to go but I am afraid he will relieve himself before flight (as it is natural for birds to do). My hesitation also lies in the fact that I dont want to reverse any previous potty training efforts if he does his business pre-flight to perch. Any suggestions on how to do bridge this training gap? And how do I reward for this behaviour if he does perform the desired result?
Thanks,
Wayne