I used a combination of Gruyere, Rembrandt Gouda and cream cheese. Just Gruyere in the cheese crumble that goes on top (more complicated than the mac and cheese itself). Have you seen the Modernist Cuisine at Home book? I've been making tons of stuff from there and I can improvise a little as well when I really know the subject.
Take the Wellington, for example. I used MCaH techniques and combined them with about five recipes I've seen around the internet. The beef tenderloin is cooked sous vide, then seared, then I brushed it with horseradish mustard (there's a local brand here in SoCal that makes a killer one), then I put it in plastic again and drop it in an ice bath to cool it down.
In the meantime, the duxelles is about 700g worth of portobellos and a medium sweet onion, and some fresh thyme; you just cook out all the moisture from the mushroom and you're ready to go...
Ok, wait, at this point I should probably just write it up for reals and PM it to ya.