There is no existing option for that in TeamCity (as of TeamCity 8.0.1).
Your options here are:
- create a base build configuration template and 4 build configurations which inherit from this template with different setting for environment variables
- use a manual triggering of the builds, but alter the value of the environment variable on build start (use Run custom build dialog for this)
write a custom TeamCity plugin which would allow to run a bunch of builds with appropriate variables set
Regards, KIR