OK! I called the Wheel Peddler, a way-cool mobile repair bike guy who is not only nice, but very supportive of local cycling events.
He'll take the XT and build me a wheel on some 717s, which he says are stronger than the 317s (517s are not made any longer)
It'll cost me a bit more than I'd hoped (but what doesn't?)
Fortunately I have only two more commute days until Christmas break, which I think I can make on my cracked rim (fingers crossed) while I wait for the new rim to be shipped in from across the country.
Thanks for helping me spend my money!