You can use any good quality riser, actually.  PCIe x1 still has more than enough bandwidth for hashing.
I use these risers for everything, even on x16 slots.
http://www.amazon.com/Micro-SATA-Cables-PCI-E-Cable%C2%A0/dp/B005G4SADY/ref=sr_1_4?s=pc&srs=2529898011&ie=UTF8&qid=1370821348&sr=1-4&keywords=micro+sata+cables