It may be simply over use of streaming video, not related to bittorrent at all, I don't know, but we need to 'fix' the problem and we've got his attention now. There is no alternative to the limited satellite service available in this rural area at the present time. If Charter decides to extend the cable half a mile up our road that might be a solution. When last I spoke to them they wanted $6000 for the install!
If you've got a Linux box in the middle you can do traffic shaping which may solve the problem - you can just keep turning the bandwidth of offenders down until they get the message or the month ends.
The fact its mostly incoming is positive I suspect - a sudden huge amount of outgoing with windows boxes often indicates infection.