I created a special 'Paste-Via', simply by adding a Padstack on the paste layer.
Then, in CAM you also select that paste layer.
Mentor fixed this circa v2007, so that IF you define a custom pad on a Paste/Mask layer,
then the SW replaces the artwork layer derivation, with the specific one.
(ie it is smart enough to figure out if a designer took the trouble to create a specific
paste/mask instance, they probably want PADS to use that instance! )
That now allows ANY size/shape of paste to be easily late-changed on a design.
If you have the paste layer define for all your decals that need paste, you can get PADS to output paste on PTH pins if you can change the CAM Document from "Paste Mask" to "Custom". Then you only output "Pads" on the paste layer, not the top.