Sadly you can't , this is a post from our Nvidia expert 17seconds whom I don't usually agree with but his opinions are very valuable and well documented :
There is quite of bit of misleading information on this topic, and generally the rule of thumb is that, unfortunately, you won't be able to enable full Advanced or High PhysX settings with an AMD card. Now, some games will be able to be played with Normal or Medium settings, so you'll have to play around with that. Some games, like Batman: Arkham Origins won't even allow the High PhysX setting with an AMD card. Borderlands 2 has been shown to generally run okay on Medium settings. Really, you need an Nvidia card to enjoy full PhysX effects as they get processed on hundreds and thousands of CUDA cores, rather than your 4 or 8 core CPU.
http://www.techspot.com/review/733-batman-arkham-origin...
http://www.techspot.com/review/733-batman-arkham-origin...
http://physxinfo.com/news/9425/borderlands-2-is-cpu-cap...