I'm confused about running an external graphics card with my MBP and Thunderbolt display

I have a new MBP 13" (not retina) with these specs,

Processor 2.9 GHz Intel Core i7

Memory 8 GB 1600 MHz DDR3

Graphics Intel HD Graphics 4000 512 MB

Software OS X 10.8.2 (12C60

My radio control airplane/helicopter flight sim runs slow. Message reads "Warning FPS to low".

I've been reading about using an eGPU but the info seems to be conflicting. Can I or can I not do this? If I can, what do I need?

This is my first Mac and with this one exception I love it. Thanks for any input you folks might provide.

John