You just use any 2:1 set up. They all come back and then the head pipes join into a 2:1 "collector". Instead of using that, you get your buddy to bend you straight pipes that run back under the bag.

It will take some "tuning" with the size of the baffles and all as you will probably want some backpressure so you don't lose your bottom end torque entirely. But it would look cool to have side-by-side exhaust coming out from under the right bag. It might make that bag a little hotter though.

 

By Jove I think you've got it!!! How about a heat shield on top of the pipes under the bag? Sounds like the perfect winter project as soon as I figure out how to design my own jockey shift setup.
I know that they make kits but I would rather fabricate something myself.
Thanks for all the great suggestions.

 

I'm fond of the heat wrap myself, but with two pipes side by side under that bag it is going to get hot and it just doesn't matter what you do. I don't think it will be dangerous - unless you keep gas or something in it. I once went on a trip and put some drinks and food in that bag with ice - by the time I got to the camp everything was melted, hot and generally un-edible. Wasn't very smart on my part.