Try this?
https://forum.pfsense.org/index.php/topic,62188.msg335842.html#msg335842
Edit, add:
As it happens, I finally gave this a try (albeit on a 2.1 system) last night, as my users had managed to offend me sufficiently (MPAA sharing violations - not only do they indicate that users have violated our policies and mean I need to find harsher controls to curb bad behavior, they also irritate the heck out of me…) and while I had some limited effect, I could not get any traffic into the proxy queue nor the http queue. It's all twisty little passages, all alike, in the dark and filled with Grues from a documentation standpoint. After no apparent effect from the linked method, I eventually tried using the layer 7 stuff to identify cache hits and misses and place them in queues, at (roughly) which point everything stopped working and I gave up and reverted to a saved configuration from before I started messing with the poorly documented Shaper. There has got to be a better way to do this, or better documentation of how to do this (that actually works).