it can't be done how you want mate, it's just not possible.
you EITHER need to use a rolling road, or live map it testing out on the open road.
A non road legal car, that cannot be taken to a dyno or test track for the day, is about as much use in mapping terms as a house brick.
Somebody could guess the setup for your spec list, but without testing, it's pointless.
Sorry dude. I'd suggest you pay £40 to hire a trailler for a weekend and take it somewhere.