I have two solutions
This is what I ended up deciding to do. I now have three solutions
I do most of my development in SolutionB because I like being able to easily reference and compile against both projects. I don't use SoluctionC at all other than as part of the following two build configurations
Hmm I'm pretty sure a build configuration can also build+deploy single projects, not necessarily solutions. So you could also drop sln A and sln C, and point your builds directly to the csproj files.
Ohad