he can't, tell him not to ever do that, he will loose his GC status and he wouldn't be able to file for his wife
he got his GC as unmarried, he must enter to activate the visa and go through customs as unmarried. he can return the next day to his country and get married. CR1 are for married to US Citizens. once he return to the US after getting married, he can file for his wife. the only category there is, is the F2A as you mentioned, and the process can take 2 years