[Batfish]

After reading a few other threads here and brainstorming some more I've come up with an idea that may work without physically modifying anything (thus not breaking anything :) ).

The second speed gear has one of those centrifugal force hub thingies to engage it. The hub is held onto the drive shaft via a set screw on a flat spot. The shift point is adjusted by a set/grub screw that you adjust by sliding a hex drive into a slot on the second speed gear to the set screw to loosen or tighten. If you can picture all that, you can picture my idea.
I removed the shift-adjust screw and took a normal screw with the same thread pattern, put that screw through the slot on the second speed gear and screw it in until the screw is even with the height of the teeth on the gear. This pretty much permanently engages second gear, which is stuck to the shaft via the flat spot and set screw.
This should eliminate the one-way and lock the tranny into second gear, effectively making it a single-speed transmission.

If it doesn't work out, I remove the screw and re-add the original set/grub screw and put everything back together.

I'll be trying this out later today (I hope) and will post my success/failures :)