The place where the player's level is called by the code, is not accessible to modders. It's baked into Oblivion.exe.
Maybe an OBSE plugin could achieve this, but the research would probably have to be done by the plugin author; I doubt the OBSE team has dug up that particular trigger, and there's really nothing for scripters to do with it, so it won't be on their current agenda.
Now, there
are tools in OBSE to manipulate leveled lists and creature definitions, and it's technically feasible to redesign everything everywhere to be static, then use a script to keep track of time and edit every relevant resource in the game accordingly. But brother, I ain't gonna be the one to tackle that.