I have plenty of pics on my phone if you need assistance with this. The trick? Buy three of the cheap "fork mounts" from REI. They have two bolt holes each and run around $20 apiece. Take the mounts to Home Depot and purchase aluminum bar in the length you need. Measure from eye-eye with the gear tie-downs installed in your cargo area.
The aluminum bar is full of screw holes and is bent 90 degrees in the middle. It looks like an L basically. I think the alum bar runs somewhere around $10 and the length is 3-4 feet. I haven't the exact measurements on hand.
Thread the three fork mounts on the alum bar, use two of your cargo tie-down loops to hold the alum bar down to the floor, and mount away.
I can put two cannondale road bikes (one on each side) inside and a full blown DH rig in the middle. Just use the proper fork adaptor for your hub size. If you go above a 170mm front fork you'll need to put it on the roof rack. Otherwise, buy a travel adjust fork (Marzocchi makes a 170-130 and a 180-140mm), put the fork in "climb" mode - to clear your ceiling - and roll out. If I were not at work right now I could attach some sweet shots of my triple mounts. PM me and I can sent them via text, if you are interested.
The total cost is under $100 and holds 3 bikes.