Not withstanding what AlanM said, and without delving through the good book, I don't think there is any actual phraseology, and to be honest, I've never been party to "delimiting" a radar service. The only way, in my experience, that it might occur is upgrading from RIS to RAS at the pilots request.
Just out of interest NS, how did you know that you were outside the "envelope" of a limited radar service?, the limitation is imposed by the atco, and only they would know when the service could technically be upgraded.
Not trying to pick a fight, just curious.