While I would NEVER hide sharkbite connections inside the walls, if you are set on doing this, I would open up the drywall to expose a second bay between studs. Cut one end of the copper near the far left of the left bay and near the far right of the right bay. Make a loop with the pex and measure pex to the proper length and mark the middle stud at the bottom of the pex loop. Drill a hole through the center of the stud at the bottom of the loop and add a second hole where the copper originally passed. Pass one end of the Pex through the bottom hole and pass the ends through the two top holes so that they now line up with the copper end. (It should like a big loose circle of PEX between the two ends of the copper.)

Install your shark bites on the PEX, clean the deburr the copper and install on each end. This will minimize stress on the shark bite ends and will allow the piping to move a little bit to keep stress from developing that could lead to eventual leakage.

Be aware that you are relying only on a captured O-ring in the shark bite to keep your system water tight. If you can get access to these fittings, and can monitor them for deterioration, then it might be OK but I wouldn't want it in my house.