?

 

Sure. Get lucid's rear speaker harness, and instead of running the new rear channel output wires to a set of rear speakers, run them to an amp with speaker-level inputs (or use a line-output converter to give you RCA's). Run your sub off of the above amp. Just realize that when you use the fader on the HU, you will be increasing/decreasing signal going to the sub rather than a set of rear speakers.

 

If you end up doing that, let us know how it sounds.

 

The PAC (Line level converter) sounds alright but you will never get the same sound quality as with a new deck with pre-outs
just my 2 cents