Fishmonger, I'd call Yosemite on the phone.
Phone menu: 209-372-0200
Within the menu, Wilderness Permit info menu: 3
Under that menu, the Public Info ranger is: 5
At 3, 6, it gives info on obtaining a permit, but you are looking for a special situation. I think the recording said permits were available through the end of Sept. So ask the public info ranger about October. They might try to discourage you, or they might agree to mail you a permit.
Please let us know what you find out.
answer received from Yosemite - the ranger station will still be open on Oct. 3, and if it should close (e.g. in April when you enter on ski) you are to self-register at the ranger station.
Interesting - I wonder who in winter would ever know that I am on the JMT if I left a piece of paper at an unmanned ranger station explaining my plans
They also said that in the future, there may be a way to self-register closer to Tioga Pass. Since my trip was planned go go over Mono and Parker Pass, the TM ranger station is actually 3 miles out of the way, but that's manageable.