From my early days as a trainee ATCO I was taught that dummy filing was not allowed for two main reasons:
1: It obviously 'clogs' the system and reduces capacity.
2: If filing using another callsign so you don't get 'spotted', there is the potential for callsign confusion with A.N. Other operator, with your randomely chosen alpha numerics.
I prefer to do it properly, but on very rare and few occasions CFMU/Swanick have suggested a dummy which has worked.