I'm looking at possibility of fenders for a Cannondale Quick. It seems that I will have difficulty mounting the rear because I'm using the only attachment point available for the rear rack. Am I looking at this correctly? How do I resolve?

Slightly longer screw, and use the same hole for each.

I have the same issue on one of my bikes and it works just fine. Mount the fender on the outside.

I agree with tsl, I had to do the same thing with my Specialized Sirrus which also had one mounting hole in the rear. Make sure the screws you get are size M5 and stainless steel.

Just use those rubber p-clips that come with rear racks - you can get them at any hardware store in the electronics section. You can put them around the bottom of the rear rack, or on part of the frame, or wherever looks good.