I would have been tempted to deposit the $2,700 check -- maybe in the trust account I am required to maintain, but seldom use -- and ask him how he wanted the $2,400 credit used.  

There is no forosphobia in the DSM-5, but there should be.  Many of us have clients who suffer from fear of taxes.  Perfectly normal people who walk among us, but resist filing returns even when due refunds.  They deserve our sympathy, but not much of our billable time.