I was on my way to a class, drift-thinking about the valleycon offer to BSG, when I realized how I could do this. I was wrong
but close enough to being right to get it in the almost-totally-working state it's in now.
I've committed it to CVS. A ship's ability to glide is toggled via a "Glide: YES" option right after "$Slide decel:", right before "$Warpin speed:".
The default key to toggle it is Alt-G (You will have to set this manually with existing pilots, see the "Ships" tab). There's no visual indication as of now, except for the speed bar going haywire and the ship gliding.
AI won't use it. I consider it incomplete but usable. I'd like to fix the speed bar, and make it so that the ship doesn't immediately change speeds. However I don't completely understand the physics code, so I'm reluctant to start making changes to lower-level functions to fix it.