In Britain, we deal with this problem partly by allowing proxy voting, where you can expressly authorise someone else to vote (in person) on your behalf. I had

In Britain, we deal with this problem partly by allowing proxy voting, where you can expressly authorise someone else to vote (in person) on your behalf. I had to do this once when my wife had an unexpected business trip after the postal vote registration deadline had closed. It's obviously not ideal from a vote privacy point of view, but it does provide a useful solution to some of the corner cases preventing voting in person or by mail.