So, first I wanted to add LED bulbs to the existing turn signal bulb.
Then I was hoping to find a dual-filament solution, so I wouldn't have to drill a hole and risk a questionable result.
NOW, I'm discovering an all-new (to me) situation: the new GTS lights appear to have TWO turn signal bulbs in each housing, and my 2007 was an earlier model with only one bulb.
So, this changes everything. Now I can make one of the bulbs the running light and keep the other for the turn signal. I'd have to test if these bulbs alone are bright enough, and find a way to wire them so the blinking turn signal is visible (and voodooscooterparts may just have the wiring solution).
This is what I found:

Left is the "old" one-bulb version, right is the "new" version.
And, unfortunately, there's a catch with this new version: it sits so tight that it seems to damage the paint on every GTS that has it installed. I'll make a separate post about that.
Next steps: wait for my LEDs to compare those with the existing bulbs to find the brighter one, then probably buy two new housings for two bulbs and wire them appropriately.
Voodooscooterparts, are you listening? There's an adapter to be built
