Partial mask increment

[JoHnDoE]

I  need a partial increment for a mask, but I don't know how to do that.

-1 ?u -2 ?l?l?l?l -3 ?d?d 

I only need to increment mask -2 (4 to 8 characters -  `Aaaaa00 ~ Aaaaaaaaa00` )

Can this be done using a mask or do I need rules ?

Any help much appreciated!