I believe the answer depends upon which version of PADS you are running. I see "pads_alphanumeric_tg.pdf" in my pdfdocs folder from V2007 but I thought they changed it again after that.
You need to disable the pin mapping as that only works with numeric (sequential) pins. Then you define the pin mapping in the 'pins' tab instead of the 'pin mapping' tab. Obvious, right?!