The exwsAllocate step uses a template to compute the final workspace path on the disk. It may look as following:
$physicalPathOnDisk/$jobName/$buildNumber

The user should be able to provide a custom template, e.g.:
String myTemplate = '$physicalPathOnDisk/$myVar'
exwsAllocate: diskPoolId: 'id-1', template: myTemplate

Additional details TBD.

For reference, see: https://github.com/martinda/external-workspace-manager/blob/master/README.md#template