You'd have to PROVE your relationship to the driver. When I'm in the jeep (white plate) and Linston is driving I can prove my residency history and relationship to him. I'm also insured to drive it.
When he's driving in the red plate the "off duty" sign is in the window.
One time recently I was in Ricardo's car (my son in law) and we were stopped in a routine document check. The officer asked him in patios who I was. I immediately answered in patois "i'm his father in law". We were free to go with no issues.
But the key here you'd HAVE TO PROVE a real relationship with the driver.
Cap