You say "not got pulled yet" Does that mean you dont actually own the plate? Or just its a pretty out there number plate and you expect it to be suspicious to the plod?
Either way. Fair play. You either have balls of steel or very deep pockets.
dont keep originals in the boot, that shows you know its wrong, when they do catch you just let them explain how its not legal, be all apologetic and normally you just get a warning and told to sort it out
i used to get told off more when they caught me parked in town, only got pulled once but that was a blind copper that thought i didnt have a plate at all. i got fed up in the end an just fitted semi legal ones instead, just normal plate but with no bs mark or post code for a cleaner look