I almost started this thread myself a couple of weeks ago as I bought the same bindings with a pair of K2 luv bug for my daughter. Ours is not the fastrak2 version but I bet the forward pressure mechanism is the same.
At first I had no idea and searching the internet didn't give any answers. Then I noticed the that the liftup-tab has a line on it and that there is a subtle raised section on the binding right next to it. The raised section moves back toward the liftup-tab line when the binding is pushed back by the boot. The spacing of the tabs is 4 mm and the width of the raised section is 5 mm so there should be a tab setting that puts the liftup-tab line inside the raised section with the boot in the binding when the forward pressure is correct. This is only my educated guess so hopefully someone with the tech manual can chime in and confirm.
Felt kind of stupid to have missed that since it's very obvious when you first see it. To my defense all my other bindings (look/marker/salomon/fritschi) have adjustment of forward pressure by a screw and the screw should be flush with something when the pressure is correct.
A shame that marker doesn't share their tech manuals on the web like salomon and look/rossi/dynastar...