Mask User url with dynamic temprorary user
It's very unlikely; this sounds like a very specific use-case that wouldn't need a dedicated project. You're going to have to implement your own custom module to pull this off.

You could go an aliasing route in a manner similar pathauto but that is likely to leave source paths open (e.g. user/XXX) to accessibility. A better approach is to create a simple module that:


Uses a hook_cron() implementation to generate random hash to UID mappings periodically and storing them in custom table.
Implementing a hook_menu() to generate a dynamic path like user/%random_hash that maps the random hash paths in #1 to a user profile page (generated in the the same manner like user/%user)