Unless Friz's frames have been drilled out, there are stops for the ferrules where the cables enter the frame. With exception of the carbon Session, all of Trek's internal routines are the same.
Without the tube it isn't too hard to route a cable. Go to your hardware store and get a length of flexible tubing thats big enough to run some cable through it. Then just fish it through. I'd do it without anything mounted to the frame so you can maneuver it around. Then when you're ready to run your cables, simply feed the cable all of the way through your tube, then pull the tube out. Presto, cable is in there. Make sure you run the housing to the shifter FIRST.
Rear derailleur goes on/through the down tube. Front goes through the top tube. Make sure you use ferrules.