Yeah, you should be able to assign another IP on a different subnet to your second interface. From there, you can configure your machine to bridge traffic from the second interface onto your primary (the one connected to the router). From there, just manually assign your PS3 an IP in the same subnet as what you gave the secondary interface on your PC, set your PC's IP address as the gateway on the PS3 and you're all set.
The specifics of how to do that on Windows are up to you though. I'm sure connection sharing to PS3 isn't anything completely uncommon :thumb: