I just took a look at HealTech's site and saw the GiPro DS series GPI. It looks to be PnP. Is it? Where is the diagnostic port that it plugs into? I like this idea.
V65S owners: do you remember what Honda's GPI showed when in Neutral?
Addendum: I found the installation instructions:
https://healtech-electronics.com/docs/GPDS-H02_Manual_en.pdf
Because the ST doesn't have a Gear Position Sensor it seems some calibration is involved and the indication either disappears or isn't accurate when the clutch is pulled in. I think I could live with that.
According to the Healtech Electronics compatibility chart, for 2003 - 2007 the GiPRO-X Type is compatible with our ST's. For 2008 - 2012 the GiPRO-DS series is compatible.
https://www.healtech-electronics.com/products/gpds/