When I mounted the my H100i to the top of my case, I used real short screws to connect the fans to the radiator by going only through the... I guess you'd call it the bottom part of the fan, the lower flange perhaps. Used some real small washers too to be sure I didn't pull through the plastic. Then used normal (short, course thread) fan screws through the case to connect the fans to it. Was a little worried about the weight but w/ 8 screws I'm sure it's fine.
That's hard to explain but - sounds like your'e thinking the same thing, and if so LOL it does work. You can mount one side of a fan to your case, and the other side to a radiator. Just don't strip any threads and it'll be secure.