I can't say for sure, but I would guess that you could just copy your entire Sins folder. Then, if you reinstall, you can replace the un-updated version with the copy.

I recently asked a similair question on the Impulse forums as I have the game on 2 machines, one with internet and the other without, I was wondering how I could back-up the patch in order to take it to the PC with no connection.

I was told to simply copy the whole installation directory onto a stick, and simply copy the lot into my Programs Folder. No installation, nothing. It works, you can even run it from a USB stick.