Lets get the facts straight....you suggested he buy a new wheelset over installing a freewheel onto a track hub. You clearly were suggesting that he should not run a freewheel on fixed threads. The suggestion of buying a new wheelset is absurd. Using a BMX freewheel on a track hub is as "proper" as using a track cog. They both are the same thread-size and, given the same number of teeth, exert the same amount of torque on the wheel. There's nothing magical about a freewheel that makes it more prone to stripping threads. In fact, a fixed setup is more prone to stripping threads than a freewheel due to the possibility of repeated tightening-loosening.