using multiple autofills in same worksheet

Hi, I was wondering if it's possible to use multiple types of autofill in the same worksheet. I'm actually using Excel to build a footprint for a module, so it needs to show an array of pin numbers. Here's a snapshot of my array:

A01 A02 A03 A04 A05
B01 B02 B03 B04 B05
C01 C02 C03 C04 C05
D01 D02 D03 D04 D05
E01 E02 E03 E04 E05
F01 F02 F03 F04 F05
G01 G02 G03 G04 G05
H01 H02 H03 H04 H05
J01 J02 J03 J04 J05
K01 K02 K03 K04 K05
L01 L02 L03 L04 L05

It will automatically increase the numbers with a fill to the right. And I can create a custom fill to "increment" the alphabeticals going down (notice that not all letters are used), but I can't do both. If I create my custom fill list first and then do a fill down of the first column, that looks fine, but then when I try to fill to the right incrementing the numbers, it won't do that now. Any suggestions as to how I can be able to choose which to do? This would have to be a repeatable process. Currently I have to manually enter all the x01 entries all the way down, then fill to the right.

Ah, that's the trouble - there is no max value. And it will never have the same number of rows and columns each time this is done. AND I can't start in column 1 row 1 because of some other programming being used other ways in the overall worksheet.