Adding Treble to Line Booster (with a switch)

Hey Forum! Long time lurker, first time poster.

I built "The Piledriver" from the MOD Kits DIY site but I put a bit of a twist on the case.

View it here:

I really like the sound of it but I wanted to also have a treble booster and I was reading about people modding their Line Boosters into Treble Boosters but I was wondering if anyone knew how to make the mod attached to a switch?

Here's the schematic:
http://www.modkitsdiy.com/sites/default/files/product_files/The%20PileDriver%20Schematic.pdf

Any ideas?