I've had a couple installations where the tire-fender-fork crown clearance has been pretty tight so to gain a few extra mm I've used one of these couplers (dremeled down) with a daruma (also trimmed down), so I can use a cap-head bolt from underneath the secure the fender. I uses a bit of lock-tite on the daruma/coupler connection.
A little fussy, requires some trial and error to get the lengths all right, and probably kind of silly just to gain a couple mm.. Maybe better/easier to just rivet/bolt
one of these to the fender in the right spot...
Here are a some details of the 'spring thing' and the epoxied reinforcement (please excuse the dirt...):
And finally, if you haven't already found it, there's a wealth of knowledge about fitting fenders
in this blog series...