Even if a narrow mounting ring would fit under the strings, I think it might still be a bit smaller than the Fender humbucker. And you'd have to drill a couple of holes in the scratchplate so it'd be ruined anyway.
I'd probably get a new scratchplate, but I agree it'd be a shame because the Fender humbucker looks very cool.
What about getting the Fender pickup rewound/rebuilt by BKP? It would cost almost as much as a new pickup, but worth it I think.