Since enabling the demos is just one small step of a bigger planned feature I highly recommend you to find a way to make it happen, I know that not everyone can store months of demo files but at least a week should be doable for every server admin.
@bil You would have to make a GSC script in order to do this. Use this code
self setperk( "specialty_unlimitedsprint" );
self setperk( "specialty_movefaster" );
in an onplayerspawned() function.