One of the big challenges in the whole “build once/deploy many” ideology is the need for environment configuration. And this is true with SSDT-based database deployments. Happily the variables are stored in the publish.xml file.
And so today's release of PoshSSDTBuildDeploy added a switch on the Publish-DatabaseDeployment function. When included, this switch (getsqlcmdvars) will attempt to resolve SqlCmd variables via matching PowerShell variables explicitly defined in the current context. The drawback here is that all SqlCmdVars have to exist in the current context. See the readme for more details.
I'm still planning on adding generate script and report options, as well as a bit of tidying up. Should all be done by the end of the week.