He can get married Islamically ( Nikah ) only and as long as he doesn't register with the kafirs law.
he can get his ass out of the kafir country then. he has to follow the laws of the land he is living in.
even if some punk get married 'islamically' and authorities find out, he goes to the slammer.
secondly, islam says equal rights does it not, and if she is not 'legally' his wife, she has zero rights, and well thats not the same as equal rights between wives, so he cant do it islamically either..oops.