First close The Bat!.

1. Start regedit
2. Find The Bat branch in registry
  HKEY_CURRENT_USER\Software\RIT\The Bat!, and
  \Users Depot inside it

You'll see all you accounts and home of accounts listed here:

User #n
Dir #n

pair of keys for each account

Key "Count" define total amount of created accounts (zero-based - I have
12 accounts, but count have value 11)

3. Add 1 to "Count" number and create additional fake account:
add keys "user" and "dir". Number for new account will be count+1 (in my
case, as example, for 13-th account Count will be 12, but keys names
"User #13" and "Dir #13"). You can use any free username, and leave
dir value empty - default location for account will be used in this case

4. Save changes
5. Start The Bat and login under created user - you'll get
administrator's rights in The Bat!