Not sure about standard Pipeline scripts, but in a Declarative Pipeline script, for a given global variable built via:

Jenkins -> Manage Jenkins -> Configure System

Name: MYPATH 
Value: ${WORKSPACE}/../path1/${JOB_BASE_NAME}

...
stage ("stage left") {
    steps {
        echo "MYPATH is: " + MYPATH
...

The output in the script is:

[Pipeline] echo
MYPATH is: ${WORKSPACE}/../path1/${JOB_BASE_NAME}

In Freestyle scripts the WORKSPACE and JOB_BASE_NAME values are expanded at build time. We use these as a nice way to have a few consistent job behaviors across all jobs, but without variable expansion, it seems we have to build and maintain variables in each job script.