Stupid idea here. Maybe get a separate gas can just for DEF, fill the can, then full the car.
This one is more than you need for a sedan (VWs take around 3.8 gal), but it's what I'm referring to. Silver Transfer Diesel Exhaust Fluid Refillable DEF Jug 5 Gallon STS-0777 https://www.amazon.com/dp/B07NNQXW9Q/ref=cm_sw_r_apan_glt_fabc_838B7YCW90D1G1P20GVH?_encoding=UTF8&psc=1
One of the logging companies I deliver to takes up totes that I fill up when I deliver to their yard up in to the bush then fills their equipment from that tote either directly from the tote or by filling up special DEF Jerry cans if that's more convenient to get it to the equipment. Another one uses fancy portable tanks.
First one uses something like this for the def, but different brand. Refilling the jugs that come in the cardboard is not recommended.
https://www.amazon.ca/dp/B07NNQXW9Q/ref=cm_sw_r_cp_apa_i_J397VH4AHHQBMKES718S
And the portable tanks are these. This company has lots of interesting products for DEF.
https://www.fluidall.com/def-system/def-tote/
I know lots of the totes that get delivered in Vans go out to logging and mining companies. Depending on the location of the shop and volume shipping it with an LTL carrier is cheaper and more efficient than sending up a tanker to refill totes/tanks.
No different than how your service truck that comes in to the bush will have bulk oil on board for the oil changes and topping up engine/hydraulic oil. Probably filled up from a tank at the shop, that one of the oil distributors I deliver to then delivered to your shop. (Unless it's shell oil, until next month I think)
Some Mobile refueling companies are delivering DEF with fuel as well. We also deliver in bulk to some mines. The one I went to yesterday takes ~12,000L every week to week and a half.
My rough math from your numbers say your company would go through about a tote per month. Feel free to DM me for 3 suppliers that sell in totes and bulk delivery. Even with having to invest some capital in to jerry cans and or tanks, with it being about half the price in bulk, payback period would be definitely attractive to management.