You should be able to pay your taxes without emissions, I just had to do this recently. My car failed emissions, and there wasn't any way to get it fixed before my Bday. So I just went to the tag office and paid the taxes for the year. Then when I pass emissions, I take that down along with my receipt for payment of taxes, pay my $20 for the tag and that's it. No need to reregister.

Downside is, you don't get your new sticker, but if you're out of state right now, I don't think that's going to matter.

And you can still pass emissions without a cat, most places don't check. Especially w/ OBD2, they just scan it. I've passed emissions before w/ no cat. This year I had a messed up sensor that was throwing a code.