Hi Clint, Bill, and all.
This was a really big and disappointing change for me as well. If there were no workaround it forced a complete rethinking of operating practices, but no matter how I thought about it I could not get around the concern that some QSOs could be missed if I couldn't have several instances running and instantly start transmitting with any of them. If you miss the first chance to call with 1800 second T/R periods that next opportunity is a long way off. The station may have quit or have other callers by then, or perhaps the propagation window is just too short.
Normally I am not one to solve a problem by adding additional software, especially non-free software. But I considered this mission critical. On a suggestion from VE7VV I installed VSPE from Eterlogic and that has solved the problem. I can now continue operating as I had been, with multiple instances open, freely switching between them for transmitting without worry about conflicts. I've configured a splitter in VSPE with my physical port, COM3 as input and output configured as virtual port COM5.