go in your garage get in and out of the car your your going replace bring up your phone random jobs go to race click till it asks are you sure the hold r2 and x at the same time if do right you will hear you garage door open as you load into the job (all this time your still holding r2 and x) when the menu opens up and you can change the radio station let go of x only then exit the job and hall ass for the car you only have about 8 seconds to get into it remember don't let go of r2 or it wont work also the key is hearing to garage door open on load up if you don't your timing needs work keep trying it will work.
google the glitch cant remember what its called but its there after 1.11 patch.
but like i say its just easier to get your friends info and put the cars in yourself.....