So it looks like it's dead unfortunately.The LW SDK hasn't changed that much but my own SDK has changed so much I had to pretty much rewrite the LW part of the plugin from scratch. After finally getting some basic instancing working, I discovered that this bug remains unfixed in LW2020
That's a show stopper for me. I filed a bug report with Lightwave3d about this back in 2018. I checked a little while later and the bug had been marked closed without me receiving any notification. I asked for some clarification from them and never got a response .
So unless this bug gets fixed, I'm not going to try to get AP working in anymore versions of LW. Sorry to get anybody's hopes up.