Can I unlock my AT&T Fire Phone without a SIM card?

I know that to enter the unlock code, I have to stick in a non-AT&T SIM card. I use StraightTalk which piggy backs on AT&T's network, so my SIM card doesn't trigger the unlock code screen. It just works. But I would like to unlock the phone anyways so that I don't have to keep track of my code.

Is my only option to borrow someone else's SIM card?