Comment by jordemort

If you have the privilege to pull off bind-mounting on top of a particular process directory in /proc you should also be able to mount something on top of /proc itself that will present a false /proc/mounts and conceal your trickery. I experimented a bit and wasn't able to bind a single file on top of /proc/mounts and I seem to be having trouble getting procfs to participate in an overlayfs, but if you were really dedicated you could construct a whole fake /proc by hand, or create something using FUSE to create a /proc that redacts anything you want, including mountpoints.