I tried to use an environment variable to supply a data series file, and it didn't result in any plotted data.
Support environment variables in various pieces of the plot section
I was able to use the TokenMacro plugin to allow a $variable to be specified as the series filename. The diff is in the following pull request:
Updated diff that passes initial checks is at: https://github.com/jenkinsci/plot-plugin/pull/23
Any reason not to pull this?
I just hit the very same issue with not expanded variables.