I use Blu-tack to secure it to the monitor top.
Actually I've also done the same to fix the track clip (at least I think that's what the metal thing with the three reflectors is called) to the top of a pair of lightweight headphones, so no need for a hat.
Added bonus of using headphones like this means I can also use the microphone on the headphones, along with GlovePie, to issue voice commands to the sim.