Creating Sequential Letter Generator in vba. AA AB Revisted

On my previous request on this subject I was provided a code solution that produced a string in the form of:

[Function ColXL(ByVal abc As String) As Long
' ** Covert Number to Letter Seq**
 ' * 108 to DD
 '?ColXL("--AA")
 '?ColXL("ZZZZZ")

abc = Trim(Replace(UCase(abc), "-", ""))
    Do While Len(abc)
        ColXL = ColXL * 26 + (Asc(abc) - vbKeyA + 1)
        abc = Mid(abc, 2)
    Loop
End Function]

- - - - A thru ZZZZZ.   It  works great.   Now I need to popluate a listbox or combobox with values the user can select from.

For Example:
User need 3 Seqs ID's generated.  And the last Seq ID was "C"
User inputs "3" in a textbox and the list box would be populated with "D" ,  "E" , " F" to select from.

User inputs "4" and the Last Seq ID was  "AB"
the list box would be populated with "AC", "AD", "AE", "AF"

User inputs "2" and the Last Seq ID was  "AAAA"
the list box would be populated with "AAAB", "AAAC" etc.

This would occur all the way up to "ZZZZZ"

What's the best way to do this?  
Array?
Table were I update the recordset (rowsource)?

Arrrgh.

Thanks