Nope doesn't look like you can, you'd need a ATI/AMD discrete graphics card to "Crossfire" with the on-board GPU.
Here's a quote explaining AMD Hybrid corssfire technology
"ATI Hybrid Graphics is a technology umbrella brand encompassing several technologies, such as ATI Hybrid CrossFireX™, ATI SurroundView™, ATI PowerPlay™, etc. that allow both an AMD integrated graphics processor and a discrete graphics processor to work co-operatively on an AMD based system to provide enhanced gaming performance, productivity and platform efficiency to the mainstream PC."
Just use the GTX460