How to reference attribute in a field

I basically want to make a block with a mtext that references invisible attributes to construct a part number. (Acad 2010)

This particular instance is pretty simple: the attributes are [PoleType] and [PoleNum] and the mtext will be "[PoleType]#[PoleNum]", so if the user is prompted and types "W" and "100", respectively, then the text next to the block shows "W#100".

I can't seem to be able to reference the object "Attribute" when defining the block. I can only pick "Attribute Definition", but the mtext gets fixed on the default value and won't update to the specific reference's value.

A sort-of work around is to turn the mtext into an attribute. Then I can add a field, pick the block reference as my object, and then pick the property (eg POLENUM or POLETYPE). This works for the specific block reference, and any copies of that instance, but I have to go through the process again for each newly inserted block.

Any ideas? Maybe a way of defining an attribute as a BLockPlaceholder or inputing a Block Reference or Attribute as a field without using the Object selector.

-Kris