A little update; I finished the rough-in version of this project and am waiting until a few test paddles before I make this a little more resilient with velcro, cement etc. The Sisu LV was a beast to properly outline and I've never done anything like this before, so it's ugly...
1) Measured front bulkhead from inside the front hatch b/c it was too far back to measure in the cockpit. Used 4" minicell for this piece. Moved foot pedals all the way forward to slide it in, then moved pedals all the way back to "lock" it in place. Webbing looped around piece for easy removal if necessary.
2) Measured depth of the yakima foot pedals -- 2" exactly, perfect! And then created a middle piece out of 2" minicell, with cutouts for the pedals. As you can see, the daypod forced some awkward contours toward the top.
3) Confirmed that the 2nd piece and footpedals were essentially flush. Created the final piece from remaining 2" minicell and then added 2 20-degree footrests with contact cement. This piece was the hardest to contour and I'm thinking of filling in some of the upper gaps with minicell scraps and contact cement.
The good news is, as clumsy and gapped as it is, it still feels comfortable and solid in the dry tests. Figured I'd take it out a few times before worrying about the finishes. Thanks for all the advice -- it helped me prioritize how to deal with the footpegs (without removing them).