Elsewhere I had read about using modified screws or plastic rods for a this purpose so went scrounging in my garage for suitable candidate bits of about the right shape and size. I found a strip of stainless steel, approx 3 mm wide and 0.5 mm in thick, and had the idea I could make a type of homemade spring clip. The piece was originally the backbone from an old, full-size auto wiper blade, believe it or not.... I had tossed the rubber but kept the steel a couple years ago thinking it would eventually find a purpose somewhere. Well today it did!
I measured by eye and bent it into the shape below with some hand tools to hopefully make it look decent. The "U" bends in each end apply pressure to the chassis parts to hold them secure. The short triple bend on the outside wraps around the chassis and secures it into place. The part that extends past the chassis provides a "handle" to easily insert and remove the clip.
All in all, I think the steel looks pretty sharp! The only flaw i see is the "securing" feature on the bottom sticks out a bit and might catch on something while running, however it's certainly functional enough for my needs as this Boomerang will only ever see light use. I could probably trim off that section anyway as the spring force does a pretty good job of securing it to the chassis already.
Not bad for 15 min of work and an old wiper blade

I'm sure many of us have done creative "fixes" like these over using junk that's just lying around (or, like me, that we keep on purpose, but for no specific purpose) -- please share if you've got a similar story or favorite quick fix!