One can set the compass in cruise, from GPS tracks.
In zero wind, it is obvious - the GPS track is your heading. And one can establish the wind easily by flying multiple headings at a constant power setting. Having got the wind, one can fly a GPS track which will correspond to some heading.
This would be much more realistic because one is doing it in cruise power with all avionics etc appropriately powered up and radiating their normal cruise magnetic fields.
At reasonable speeds, say 100-150kt, a light wind, more or less aligned on one's track, will make virtually no difference to just using the GPS track straight off.
The actual compass adjustment procedure is iterative. And one needs a brass screwdriver.