Was your x4 slot open ended? Mine seems to be closed. I don't really want to resort to a soldering iron like this guy: http://www.tomshardware.co.uk/forum/249291-12-card. Will probably have to get an extender cable then. Next problem is how to mount the card while still leaving the case closed... (don't want the kids to get electrocuted).
My bad, I was thinking you had two x16 sized slots and one ran at x4.
You could still hook up 3 cards if you buy both an x1->x16 and an x4->x16 cable.
Fitting them in your case may be tricky, get creative and you'll probably be able to work something out.
Extender Cables: http://cablesaurus.com or http://shop.ebay.com/cablesaurus/m.html
Or you could cut the slots: http://blog.zorinaq.com/?e=53
I personally haven't cut any slots ... I went to do it once and decided to just get the cables right before I went through with it.