what can I dilute it with to make them happy and still be usable?
Why don't you ask them?
Not about the useable part. Choose materials with widely different boiling points. Or maybe nonpolars like toluene, which if the GBL is converted to GHB salt, will separate from the water layer and can be poured off.
But, if it's government, and regulated, I imagine there's a list of specified diluents somewhere.
The best market to be selling for is probably electronics. I think they have very stringent rules about what sort of residue can be left behind by a cleaner.
However, I think they're all moving to N-methyl pyrrolidone or dimethylpiperidone.
Good luck.
It would be funny if someone sold ethyl hydroxybutyrate, or ethyl acetylhydroxybutyrate. Unscheduled, but definitely prodrugs to GHB.