Hi Terry
As no one else has come up with anything, I have something but she isn't the prettiest gal in town - but then neither is sendkeys.
It looks like the plugin is blocking - which may be for good reason - who knows? Anyway, the idea is to spawn a thread outside Mach and execute sendkeys from that. In the .m1s fire the .vbs and THEN fire up your plugin - as written, 5 secs later sendkeys will fire. Season to taste.
You'll see the .m1s is coded to call the .vbs in c:\ - you'll probably want to change this to somewehere under c:\Mach3 or whatever.
Assumptions:
You have the windoze scripting host present and enabled.
The plugin dialog sets focus properly and has a tab set (if it's needed).
I thought twice about posting this cos you could do some truly nasty things with it if you feel like being creative - but as ever - if it breaks your PC, your machine or your heart you get to keep the pieces.

Cheers
Ian