Urs and Fredrik, thanks for input on this -much appreciated.
I'm going to think about stem-distribution for a few days and see if a good solution comes to mind.
Urs you raised the issue of horizontal spacing in the snippet... perhaps just using a very short base duration for the stemmedGlissando will help here?
As for now, I've re-jigged this a bit to make it work more like \afterGrace, as I think they are sisters.
Overall it should be more robust and it appears more in line with how I usually see these things notated in scores nowadays.
all best,
piaras