I have a noctua uh12F which is a similar design. I would recommend mounting it outside the case.
The first time through went something like this: take out m/b, install CPU, install backplate and brackets, install ram, mount h/s, mount fan with clips, stick into case and fiddle a bit to plug in cables and wires. Mounting the backplate was the hardest part and only required 10 minutes. Total time 1 hour being overly careful.
(I then had a bad overclock setting that froze the whole deal. couldn't figure it out and took the whole thing apart leaving the m/b in the case.)
Second time went like this: cpu in; plug in wires and cables; mount h/s; curse and swear as I cant fit my hands in to hold the spring tensioned screws while i apply ridiculous amounts of pressure while not trying to break the board or bend the h/s; get one screw in, curse and swear as other screw wont even come close to reaching the threading; mount fan and one spring clip, curse and swear as other clip wont even come close to snapping into place; wrestled clip in place with giant set of plyers and medical forceps; went on shooting rampage in BF2(you wouldn't like me when I'm angry, joke); came back and assembled rest of system. Got to post and boot up, went to bed. Total time 4 hours.
Once you have the h/s mounted, it has a better hold on the m/b than you will ever have. I feel comfortable using it as a handle to slowly lower the whole deal into the case. Besides this type of h/s doesn't really weigh that much once you get it out of the packing box. Maybe thermalright has longer screws and weaker springs, but I cant imagine reaching around the h/s and being able to get 4 of them while its mounted inside the case.