I think its a lot easier than that, and indeed impactful.
I drive fairly few miles. A car can literally last me 20 years or more. I have a 2005 Honda with 62,000 miles on it. Nowhere near needing to replace it, nor has it needed a thing other than scheduled maintenance.
Instead of trying to fiddle with depreciation, lets use consumption and replacement.
Were I to become an Uber driver and handle a modest number of fares, that 20+ year replacement cycle could be consumed in 4-5 years. I hardly bother to wash or vacuum the car, but would have to do so regularly so it would be presentable.
A 25-35 thousand dollar expense (forgetting about gas, insurance, wear and tear, maintenance) is a big nut to crack.
I'm watching a version of this happening right now. My ex-wife commutes 350 miles to an area that pays more than she can make around here, and stays in an AIRBNB while she's there for 4 days, then she commutes back. She's putting an additional 30,000 miles per year on a top of the line Lexus and intends to replace it with a similar car when its worn out. In four years she'll have to lay out another $70K+ for a car. If she worked locally, the car would last her 12-15 years.
I'm pretty sure that adding in AIRBNB costs and so forth neutralize her extra pay, but critical thinking isn't her strong suit.
This line of thinking, car as a capitalized asset with a specific cost and period of useful life seems more sensible than trying to bring it to a per mile depreciation calc. While a car depreciates when not in use, a seldom used car lasts a LONG time.
I've done the Uber/Lyft calcs on this basis, as I have free time and a clean, reliable car...but it still turns into my having to replace the car more often than I would otherwise, and those replacement cost figures swamping anything I'd make.