Combination of smoke pot, night light, and plugging the entry holes after sundown will do the trick, then build a bat box for the poor darlings you've evicted assuming you still want their help in ridding the environs of skeeters and gnats.

And how come nobody has mentioned Brian Lies' children's book, Bats at the Beach, which has the bats entertaining themselves with banjos and other b-things? Lies has two subsequent books (for bats at the library and at the baseball game), but beach is his best.