I can't say from experience as my aluminum pot is less than 4mm thick (maybe 2-3mm) but I think I've heard of people successfully mount an element with that thickness.
For my own experience, I have that 2-3mm thick aluminum pot, a normal heater element with the typical threads, the typical SS locknut and typical silicon oring. Most people, I think, do not include the black oring that comes with the element, however I do have mine on still, on the outside of the pot. So I technically have an extra 2-3mm worth of oring padding it up.
It wasn't EASY to screw the nut on, like the initial grabbing of the threads was really awkward to get going, but once I had it grabbing I could thread that sucker down a number of turns until tight.
So probably you'll be fine, and if need be you could also use a grinder or slightly larger hole saw to make the area of contact for the nut, oring, etc. LESS than 4mm. You could definitely DIY on that with a dremel or the right sized hole saw.