I've seen myself some cops placing MPCCs in bad places or far from the city just to troll and you can do nothing to solve the problem. Not even adding him to /ignore (which was supposed to ignore everything from him) solves it.
I would like to suggest two different methods to prevent this from happening, and will be up to players to decide what to do:
1. Adding the player to /ignore should disable spawning on his MPCC (either using custom spawn or rapid transport).
2. Adding a new setting called 'MPCC custom spawn' (where you can disable all MPCC spawns or an specific account) or adding an argument to 'Ignored Custom Respawns' so you can add an account (e.g: MPCC:V4MP1R3) so you won't be able to see my MPCC custom spawn.
What kind of criteria your suggestion holds: Reduces an inconvenience.