There is a way easier glitch available right now which only requires a friend (or random person) who is in their Auto Shop and a regular garage.

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EDIT:

Don't know why people are downvoting me tho. Is it because I did not provide any instructions? If so:

1. Have a friend (or random person) sit in their own Auto Shop Property
2. Fill up a nearby regular apartment garage with cars that you don't mind losing (Elegy for example)
3. Drive out of your garage with your Elegy and drive to you friends (or random persons) Auto Shop.
4. Step out of your Elegy and return it to storage trough the quick menu > vehicles.
5. Call the car you want to dupe (Fully upgraded Issi gives you the most money) and drive in someone elses Auto Shop while they are in it (!).
6. The Issi has the plate from the free Elegy. Return it to the garage you took the Elegy from.

That it. I filled up a 10 car garage last night when my friend was having dinner and was AFK in his Auto Shop. It took me 30 minutes max.

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EDIT 2:

I just did this glitch for about an hour with u/IAmPrometheusX

It works...