I've been using friction rings instated of jib cars for over a year now its a slightly different setup and was only meant to be temporary after ordering a new jib to tack though the staysail gap the jib tracks I wanted where out of stock but its work so well I'm sticking with it.
The jibs sheets run through the friction rings back to a block and pad eye and up to the winches, the friction ring control line is attached to a block on the chainplate and runs back to turning block and up to 2 small winches behind the cockpit which where already there, I can adjust everything from the cockpit no need to go forward, the jib sheets have never fouled during tacking the whole set up cost less than $50 and didn't need to drill any holes