Fusel grain oil is a wonderful tool in a Flavorist's tool box. Natural sources of raw materials is a big deal these days.
You might check with flavor industry raw material vendors like Sigma Aldrich Flavors, Penta Manufacturing, Vigon International, Advanced Biotech, etc. Many flavor and ingredient manufacturers have to purchase products from approved vendors so the vendors may be the ones to approach rather than flavor manufacturers.
If this is a viable option, they will work with you on how to pack and ship since fusel grain oil is considered flammable.
Another option is to call a hazardous waste company who can pick it up and dispose of it. It's an option.
~Susan