I wouldn't suggest filling it with foam, but maybe a air bladder.
My point is that we have created a design that allows for a hell of a crumple zone if you ever mega piton. Because we have no holes in the shell to attach a foot brace, there is no "one to one" contact to your ankles if you piton. Meaning that the entire Unishock bulkhead will flex forward, as you piton. To the point that it will go to the bow of the boat if need be to save your akles. Filling it with foam will eliminate that feature. May not be super important for you in particular, but it has saved me twice now and I was glad that was there both times.
An air bladder would solve both issues and still flex/fail if indeed you hit that hard..
Regardless if your boat is a demo or not, be sure to check if you have plastic or an aluminum foot brace behind your foam blocks. If "black plastic" then you are stoked. If aluminum, and no obvious hinge, then yes, you are not going to have that feature. The aluminum model with the hinge was very expensive and we didn't use them in demo's.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body. But rather...To skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming... WOW !!!! What a ride!!!!!!"