When I went to install this, I noticed that in my templates (latest vB version) there's an additional line that's not listed in your first deletion recommendation:
<input type="hidden" name="securitytoken" value="$bbuserinfo[securitytoken]" />
So, I'm adding it where I think it belongs and giving it a shot. I'll report back.
Thx! This is exactly the mod I'm looking for.
Edit: Works fine, except for the missing Prefixes dropdown.

Must troubleshoot.
Edit 2: Oh wow, another version. Guess I'll have to try that one now.

Thx! Moving to next mod... (Thanks, Kira.)