I'm sure you could come up with some sort of reversing mechanism to mount to your frame tube that would push the shift lever downward as you pull up with your foot. Possibly you could even do some internal mods to the tranny to reorient the shift pattern of the transmission itself. I think the second would be pretty tough (financially) to pull off.
If it were mine, I would mount a shift lever independently on the frame tube with an actuator arm that protrudes off the
rear of the shift lever. Connect lever to a modified shift lever in the original location with a protrusion off the
front of it. That way when you lift
up on your shift lever ( the new independently mounted one) it would push
down ( via the rear facing protrusion)on the front facing protrusion on the original location mounted lever causing it to push down,which would correlate with standard Honda shifter rotation,therefore reversing your shift pattern. You would have to build offset into the independently mounted lever to clear all of the working linkages and also to place the lever in a location comfortably reached from the stock foot rest location. There would more than likely be a certain amount of trial and error involved in finding which pivots points, linkage angles and leverages ( length of shifter protrusions) worked out the best to provide optimum shifter lever travel vs. shifter lever effort required. Especially considering the fact that these bike's original shifter levers are very short in length,and package tightly against the engine case, it leaves very little room to mount such a mechanism.It would be quite simple to achieve,but very hard to relate via text. Does that help any?