I do agree with the concerns you have about this. It's weird to fully duplicate the procline-setting function of Qless here.

Qless doesn't update the procline on a per-job basis, and the point where it sets the procline is before any job has been reserved. See https://github.com/seomoz/qless/blob/master/lib/qless/worker/serial.rb#L23

This means that accomplishing this is hard to do without either modifying qless or setting the procline yourself.