So I found out recently that any PCI-e x16 video card will fit and function in a PCI-e x1 slot (just as long as it's not superbly heavy); it will just not run at full potential. That said, I'm wondering if it would be worth it to use a low-end video card, like one of these just for dedicated PhysX:
-EVGA GT 220 1GB 128-bit GDDR3
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130522&cm_re=nvidia_gt_220-_-14-130-522-_-Product
-MSI GT 430 1GB 128-bit GDDR3 (probably leaning towards this one)
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127541&cm_re=GT_430-_-14-127-541-_-Product
Cheers!
-EVGA GT 220 1GB 128-bit GDDR3
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130522&cm_re=nvidia_gt_220-_-14-130-522-_-Product
-MSI GT 430 1GB 128-bit GDDR3 (probably leaning towards this one)
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127541&cm_re=GT_430-_-14-127-541-_-Product
Cheers!