You can also buy PCIe 16x and/or 1x extenders.
I was able to pick up a few here:
http://www.cablesaurus.com/I'm able to run my cards on a board with 2 PCIe x16 v1.0 slots and
1 PCIe 1x slot.
If you use the extenders you'll have to find an alternative way to
mount/support the cards since they won't be slotted directly into your
motherboard. I built a frame using PVC pipe and hang the cards
from it using zip ties.
Good luck,
Matt