What I have been doing to teach my dogs to go both ways around barrels is to set up two barrels. I send the dogs in a figure eight pattern around them, with the dog going between the barrels to start the figure eight. They then do the figure eight around the barrels. Then I will do a figure eight which requires the switch, by sending them to the outside of the first barrel to start. They will then come through the center and need to do a switch to go back around the second barrel, come through the center, then another switch to go around the first barrel again. This has been working for my dogs, they caught on to it quickly.
I haven't tried the switch around a barrel on a course yet since I haven't had the chance but I'm guessing it would transfer easily.
Anne