This has been solved in 1.7 which was released today. It was fixed for all support schedulers, including SLURM.
To enable it, use the copy_environment attribute in your script element. The given scheduler will set the appropriate flags.
In slurms’ case it appears that you also need to set job_environment with at least something.
This configuration in SLURM:
script:
copy_environment: true
job_envorionment:
FOO: "BAR"
will produce --export=ALL,FOO when submitting the job.