[Koha] Hourly Charge using Koha

First off, thanks for this wonderful program and wonderful support. We are trying to get Koha up and running to replace an old Winnebago system they have in place. Most of the transistion seems to be going smoothly, but we've had a few unsolvable questions. The most dire question so far is this: Our Library consists of mostly video tapes / DVD's / audio tapes that are checked out to students for 2 hours maximum, so they can watch them in a computer lab. We would like to modify the late fee charges so that they are charged per-hour of being late, instead of the whole day. Would this be possible in the current charging configuration, or would we have to modify the charging script to accomplish this type of biling? Thanks again, Jim V