NY was thinking very hard :
There only seems to be a postal vote (in which case you need to still be here
until the ballot paper arrives) or a proxy vote in which case your proxy
needs to be someone local who votes (on your behalf) in person.

OK, so we're in an area where our votes will be pushing against an already
open door, so we'll just increase the votes for the foregone-conclusion
candidate, but it would still be nice to vote. There's time enough yet: we
don't leave until a week on Friday.

Someone could quite easily do it for you, if they had access to your
letter box. The ballot card just needs your signature, but I very much
doubt they check that simply because they have nothing to check it
against. They would only check if there were some dispute.