Well they could do this year with the prospect of a Trump 'divi'.
Normally turnout is significantly lower than presidential elections but still, more people turn out to vote at the US midterms than turned out to vote for new UK PM Andy Burnham (ok that was a cheap shot - Burnham was not voted in by the electorate).
The divi could also backfire by increasing the turnout of voters opposed to Trump making it more likely that the Republicans would lose either or both houses.
Obviously people could vote Republican just to get the divi but it's a gamble and most peoples' politics are not swayed by money - even $5000. Although if you are homeless or living in a van then $5000 could well be enough to make you a Republican for a day.
One thing is certain: Trump's divi will make these the most interesting midterms in living memory, perhaps ever.