Cash Back Debit Cards to pay Credit Card Bills?

There has been some discussion on the formerly over-moderated site about CB debit cards to pay CCs. The theory is if a debit card offers 0.5% CB, you can turn that citi Double Cash into a 2.5% (neglecting the R+ boost), if a debit card offers 1%, you can turn that 5% Disco into a 6% CB card, etc. It's not a slam dunk. Many debit cards have been thrown around. Some have spending/earning caps. Some, while offering CB in purchases, offer no CB when you make CC payments. Some debit cards don't work, and some credit card issuers don't accept debit card payments. With the upgrade rewards checking - the only debit card I have that gives CB - I did two experiments today. I made a $50 payment to my Shop Your Way citi MC over the phone using my 0.50% CB upgrade debit card. I also used my upgrade debit card to make a $50 payment to my citi Custom Cash using PayPal Bill Pay. I have yet to see if I will earn the extra 0.5%. But we'll see! But the question is, do you guys know of good debit cards that offer CB when making CC payments? And to which credit card companies? I know not all issuers except debit card payments directly and I know not all are listed in PP Bill Pay. Thank you! :)