It obviously doesn't help you right now, but it might be interesting to know that Windows 10 has the provisions built-in to support multi-client access to MIDI devices, see extract below. The full link has a lot interesting info!

MIDI Enhancements in Windows 10 [from Sep 21, 2016)]
MIDI Enhancements in Windows 10 - Windows Developer BlogWindows Developer Blog

Extract:

"In Windows 10 RTM last year we introduced a new MIDI API, accessible to UWP Apps on virtually all Windows 10 devices, which provides a modern way to access these MIDI interfaces. We created this API to provide a high performance and flexible base upon which we can build support for new MIDI interfaces.

/.../

One great feature of the new API is that it is multi-client. As long as all apps with the port open are using the Windows 10 UWP MIDI API and not the older Win32 MME or DirectMusic APIs, they can share the same device. This is something the older APIs don’t handle without custom drivers and was a common request from our partners and customers.

Finally, it’s important to note that the Windows 10 UWP MIDI API works with all recognized MIDI devices, whether they use class drivers or their own custom drivers. This includes many software-based MIDI utilities implemented as drivers on Windows 10."

Edit: That link also provides some cool info that Microsoft worked early on with Cakewalk on the Windows 10 UWP MIDI API and a wrapper for it, enabling DAWs like Sonar to implement those features faster. Cakewalk really was/is ahead in the Windows game!