Universal binary version for different versions of SSE

Can I create a universal binary for Mac OS X that contains two versions of my application that is compiled with SSE4.2 and compiled with SSE3?

In this case, I would compile the version with SSE4.2 automatically for a CPU supporting SSE4.2.

If not, I would like to receive suggestions on running my application on older processors that do not support SSE4.2, but use SSE4.2 for a processor that supports it.

Please note that I am targeting the Mac AppStore if that matters. I am using Clang with Xcode 4.5.