There's no rule against it, except, perhaps, the portion of CoC B8, which states, "Pilots are permitted to declare in-flight emergencies only when under positive air traffic control." That said, I certainly don't consider lost comms an emergency. I've had semi-lost comms in IFR (could hear but not transmit, in which case I acknowledged ATC by IDENT) and had full lost comms once IFR (that was fun) and several times VFR (RW). There are procedures for that; just follow procedures. From an ATC standpoint, I welcome the challenge and the deviation from the routine when someone simulates lost comms and/or an emergency. And I have never had anyone complain when I engage a pilot in the simulation of an emergency, even when it sometimes slightly affects other pilots (i.e. 10-15 second delay, etc.). As a matter of fact, I've been thanked several times by some of the other pilots on frequency for doing so, as it allows them to hear how an abnormal and/or emergency situation is supposed to be played out. If, however, a lost comms situation or emergency would have a significantly negative effect on others, or if anyone else complained, I'd simply ask the pilot to suspend the situation in deference to the enjoyment of the network by others. I think this approach is quite fair and certainly keeping in the spirit of the rules.
