I'm told that when pulling or pushing narrow gauge cars coupled to a standard gauge idler car or locomotive through a draw (or "swish") changing the position of the third rail, the effect on the narrow gauge cars was rather detrimental. In a discussion on this board about switching on the Antonito three-rail wye a while back, it was mentioned that the standard gauge engine and/or idler car would be uncoupled from the narrow gauge cars when approaching the draw, and then have to go clear around the wye and couple on to the other end of the cut of cars to complete the move.
As far as pulling the cars through, it seems to me that it would be a matter of uncoupling at the beginning of the draw, running around the wye, pushing the cut of cars through the draw far enough to enable the locomotive or idler car to recouple using the other offset coupler, run back around the wye, recouple, and continue with the move.
Sounds like a lot of work for something so simple.....
Ed