Honestly, it would probably have more support among Newfoundlanders than joining Canada did. I think you probably have to keep Newfoundland from becoming a Dominion, which shouldn't be hard considering that was basically just symbolic and for all purposes NL remained a Crown Colony. Then, in the 50s or 60s as decolonization sweeps the globe, NL is given the choice of Independence or joining the UK. Basically the same option that was given to Malta.