Hi guys, this has been discussed at length, for YEARS. viewtopic.php?f=8&t=4211#p18366
If you need specific code before the pause, you can use a replace command to have Simplify3D add your code prior to the specified pause height. Postprocessing scripts run prior to GPX so the G-Code will make it's way into the resulting x3g file.
If it were me, I'd read this viewtopic.php?f=8&t=1959, slice, open the g-code, find what code to use for a replace command, set it up, then slice again.
It's pretty involved, but hey thats what we have to deal with for buying printers that don't read plain g-code files.