Stagein and Stageout directory creation

I am looking to automatically copy all required files for a job from their respective storage directories to a separate staging directory using stagein. I set up a PBS template file for users that stages in the files as such:

#PBS -W stagein="/absolute/path/to/$PBS_JOBID@server:/another/path/to/testfile.fem

When I qsub the .pbs file that includes this command and it is queued, I expected to see /absolute/path/to/$PBD_JOBID be created with the staged files in there. However, it did not appear.

I have enabled sandbox=PRIVATE already.

When are the staged files copied over?
Alternately, what is the best way I can copy all necessary files to a unique temp directory named $PBS_JOBID?

Variable subsitution is not supported in PBS Directives

When a capable compute node is allocated to the job for execution
stage_in: pbs mom does the input deck copy
stage_out: pbs_mom does the output deck copy

Variable subsitution is not supported in PBS Directives