Apologies, thought I had left a response but I didn't hit submit!!
Thanks fwilleke80, I was hoping to avoid writing my own, but I might have to.
Hi r_gigante, it's a doc in memory (not a clone, but in memory none-the-less) and can't be in the active viewport. It's rendered to bitmap, sometimes very frequently. So I can't be switching to it in the viewport for one command on each frame. Is there no way to piggyback off the underlying CallCommand() functions for this? No messages I could send to try and invoke it?