Alphanumeric Number Range Territory Management

Hi--I am trying to create an alphanumeric number range for Territory Management in CRM.  I need to create 4 ranges to do the following:

Range   From     To          

2-digit   00           ZZ

3-digit  000          ZZZ

4-digit 0000         ZZZZ

5-digit 00000       ZZZZZ

So for example I could have any of the following combinations:

2-digits:                3-digits:                4-digits:

01                           001                         0001

0Z                           09Z                         090Z

A0                           A09                        A9ZZ

AZ                           A9Z                        A999

I know they need to be "external ranges" and by viewing other discussions it seems that the range should be "aa to zz" but after I create one range, I'll get an "overlap" error when I try to create another (ie, I can create "aa to zz", but I will get an error if i try "aaa to zzz".  Do you know how/if this can be achieved?