You can follow the arduino guide to add a new board but it's hard work. I suggest you use a different application name in Visual Micro and set a different "Optional physical folder for downloaded packages" (in the IDE Locations window). 

For example, if you are using the arduino 1x app then select the "Visual Micro" or "Arduino 2" app in IDE locations and then configure a path for "Optional physical folder for downloaded packages". Obviously somewhere other than Arduino15

Then you can install esp 1.0.6 into one app and 2.0.5 into another.

When using a project you will then see option to switch between the apps you have configured. It doesn't matter if you have arduino 2 installed or not. Having the arduino 1x app contributes nothing to the esp boards.

Did what you have suggested 
Glad to inform you it works!!!
I think if there will be native support for different toolchain versions like in PlatformIO it will be great!!
I am one of the biggest fans of the Visual Micro Plug-in
I promote it in any possible opportunity and force employees @ Intel who takes my course for advanced ESP32 topics to work solely with Visual Studio and your plug-in