I am the founder of this. Please show me, DRObythePoUnD420 some credit if this ends up anywhere other than Reddit.
I got it, finally. 🙂
Your friend needs to use the join mission/ finish mission/ freemode trick to make his own public lobby.
When it is time for you to come back online with the vehicle, press start, go to join friends, wait for the confirmation.
As SOON as you press X to confirm, Press your center button, sign out, press center button, let it force the sign in screen, etc etc.
ENjoy! It's working for me.
You can also used a lobby that you have lagged out of. As in, those lobbies where it says everyone left, but it was really just you. That lobby is still public. Bringing custom cop cars and the tow truck are a good way of causing this 🙂
You can also go to friends, join game and use that confirmation screen.