More phone banks.
My problem with mail in ballots is the anonymity. I don't even like to fill in the Census form. When I vote, I want it to be private. Maybe that is why the response is (partially) low.
No elected government should know which people voted for them, and which voted for their opponent.
This whole mail-in ballot thing, here, was brought about by Rick Murphy who owns several local radio stations and ran against Trent Franks in 2004.