Help with checkout directory and branches

Hi, I use teamcity to manage the CI of a game developed in Unreal. Because an Unreal game has hundreds of GB, I always use a common checkout directory to avoid having to re-download those GB or to be able to cache the compilation/shaders...etc.

I want to have support for branches, so I want each checkout depending on the branch to go to one directory or another.

The first thing I have thought is to use %teamcity.build.branch% in the Checkout Directory field. The problem is that I use PlasticSCM and the branches are /Main and /Main/BranchA. So when the directory is created, it creates a folder structure for me. The problem with this is that it creates Main folder and then inside BranchA.

Project
Project/Main
Project/Main/BranchA

It's not a good idea to have the directories nested and I even think Teamcity can cause the checkout directory to be cleaned up and that's something I want to avoid.

Another way I thought is to use a bootstrap step to do a replace of the branch and change “/” for “_”. Set an environment variable and that is the one I put in the checkout dir. But this doesn't seem to work, as the directory creates with the default variable value even before I modify this variable in the bootstrap.

I can't think of any more ideas and I don't know if there is anything I can do to get what I want. 

Something like this:

Project_Main
Project_Main_BranchA/

Thanks, best regards
Javi