I'm not really modifying either one of the circuit boards. Basically I'm going to remove the LED's from the SprintBooster board and JB Weld them on top of the SPORT circuit board where the current LED is. JB Weld is perfect for this as it sticks to almost anything, doesn't conduct electricity, and is thick enough to keep any stray remnants of soldier from poking through and touching the transplant LED's. Then I'll soldier wires from the LED's to connect them back to the SprintBooster circuit board. In other words, the components from the SprintBooster circuit board will be physically attached to the SPORT circuit board and electrically connected via wires to where they used to be on the SprintBooster circuit board.
Going about it this way enables me to retain the OEM backlighting and tactile feel of the button.
William.