How to force TestFlight to keep one Apple ID?

Let me start off with some background. My parents and I use different Apple ID's, but I use both on my phone. My personal one for iCloud, and theirs for iTunes purchases (since theirs has our family's credit card and all of our previous purchases attached). I recently starting testing a beta version of a friend's app through TestFlight, of course with my personal Apple ID. TestFlight forces you to use your iTunes Apple ID, which means whenever I want to either go into TestFlight or go to buy music, I have to switch credentials. I do not want to switch TestFlight over to my parent's Apple ID. Is there any way to bypass this constant switch of logins and keep TestFlight always on a certain Apple ID?