Yes you can. Nvidia doesn't like it though. http://answers.yahoo.com/question/index?qid=20120322171153AAeHujC
My brother said that it was a pain and not worth it. I think you would be fine with a weaker card for physx. Also, consider if physx is really worth it. More and more games are either phasing it out out making it do barely anything. Almost every game you have to look hard for the difference.