There is no such thing as "borrowing" other players drivers like you can borrow their cars. Remote Racing is where you can race one of your drivers with your friends, but you can't control them. It's simply used for gaining credits and experience while you're not playing GT5.
You can select it in Community, under your name where you have your inbox etc. it's at the bottom option. Go in there and select a race, then select your driver, add friends' drivers and click race.
More info can be found in the B-Spec forum. If you think it pointless though I guess you won't bother, but there's plenty of reasons why it's used by most people.