Well, this simple trick saved me 100 bucks on the Mono Guitar Tick. Snap-clip keychains are widely available too. The bottom part of the pedal case is not attached to the gig bag, but doesn't bother me as long as I'm carrying the bass on my back. Open for better suggestions!
I’ve done a similar thing using carabiners to attach an acoustic image head in its soft case to the back of my Mono gig bag.
A quick link or carabiner would do the same thing. I would probably use a quick link. It would keep the pedal case higher.