Just some closure, because it's annoying when somebody posts a problem and then doesn't update whether they've solved it.
Located a pex-style hose bibb at HD, some crimp rings, a pex->polyb adapter, rented a 1/2" crimper and eventually got the flange off. Here is the finished, not so pretty result. It may be the Frankenstein of plumbing, but it works and doesn't leak.
