Hello Cosmo, I know what you're saying. I've also gone through your frustration but now that I've been through it, I tackle it this way and work almost every time.
1) Switch on TGP and Mavs (I usually start with the Viper on the runway so I'm ready to go)
2) Fly out at least about 10 Nm runway heading, take your time. Make sure TGP and Mavs are up and running.
3) Make a 180 degree turn and fly back to the field. I usually keep my speed around 300 KCAS and around 6000 feet or so
4) Switch on Autopilot to Maintain Alt and heading.
5) Pick a decent target (Like a PAR or something that is close to the runway and easily visible) with the TGP as SOI
6) Make Mavs SOI, slew to target, TMS UP to lock target (make sure crosshair is closed). Try 7Nm or less, BSGT - Mav is now boresighted. TMS Down.
7) Cycle to Next Station and repeat step 6.
I suggest to try and boresight the mavs when distance is between 3 and 7 Nm to ensure proper boresightedness. I also usually move the TGP crosshair and compare with what the Mavs are seeing to ensure they're looking at the same target.
Keep practicing, it's worth it.