There just may be one - The GMA500 is based off of the PowerVR SGX 535 core from Imagination technologies, and this is the same core used in the iPhone 3GS and iPod Touch 3rd gen.
Possibly, just possibly, one can extract the drivers from the iPhone and tweak it to work on the GMA 500.
Technical info from Wikipedia:
Apple unidentified—SGX535 + VXD (Samsung manufactured), in the Apple iPhone 3GS and the Apple iPod Touch 3rd Gen (32GB/64GB)
Intel System Controller Hub US15/W/L—SGX535(Intel GMA500) + VXD370, in a heck of a lot of devices
I'm assuming the VXD in the iPhone is the same thing as the VXD370 in the 500, which is a HD decoder.