To be honest, I never got any notifications about any responses to this thread since my last post, so I didn't even know people were giving me options and answers here. :P
I know it's been a couple of months, but just for clarification:
I'm a HUGE Superman fan
I haven't spent a ton of money on the black-bagged issue
I don't intend to sell, but I do like to have the protection and safety of a slabbed comic for my more high-profile issues and signatures
Anyway, it looks like there's simply no way to get it signed AND keep it sealed AND get it graded/slabbed. I'm still holding onto some of my childhood feelings on keeping the issue sealed and bagged, so if I get the opportunity again in the future to get either Jurgens' or Breeding's signature, I'll just buy another sealed copy of it and keep that in storage so I can open the other one and get it signed.
Thanks all!