How can I fit this mudguard? I thought this would be simple.

 

The problem is that the entire brake assembly needs to be rotated to screw into a thread built-in to the fork. There's also a hex/allen hollow tube-nut at the back (see red arrows), but this doesn't do anything until the bolt has screwed through.

I was hoping to put the metal loop of the mudguard in front of the fork so the brake would clamp it tight (with a washer not pictured). But when you put the mudguard in place you cannot rotate the brake to screw it in, because the lever arms catch on the plastic mudguard.

Is there some trick to this bicycle-tetris that I'm missing or is this simply the wrong kind of mudguard for this fork/brake?
Use a hacksaw or a dremel tool to zip out a notch in the tab like this:

This will allow you to slide the fender onto the brake bolt and tighten everything down without losing vertical fender adjustability. If you wanted to add a bit of security, bend the very ends (maybe 2mm) of the tab in a vise so that it can't slide out (though, if your front brake has come loose, you might have worse problems than a rattling fender.) Make sure if you bend the tabs that you bend them away from the fork crown - sometimes you have to do this anyway to get the tab to clear the lower headset cup, but you get the idea.