Utilization dependant rules for a certain IP on pfsense 2

[valunthar]

Is there any way to set up some traffic shaping rules in pfsense 2 so that when the network is not being used for anything else one computer would be able to fully saturate the pipe, however as soon as other traffic is detected on the line the bandwidth for that computer is throttled back to a reasonable speed?

Since the traffic is mostly coming from one machine I considered using the penalty box option, but that seems to be a strict limiter rather than a flexible one. Any help would be greatly appreciated.