Rectangle Stretch as Text is Added

[Jaycee.foli]

So, I swear I have done this before, but for the life of me, I cannot remember how, nor have been able to find a forum or instruction on it. So hopefully I am not crazy. Is there a way to have a rectangle (or elipse or other shape) to stretch, as you type in text to an attribute definition? Basically, We have multiple clients, some use short numbers for tags, others might use longer numbers. I want to use the same block tag and just have the border stretch based on text length. I swear I have done this before with an tag that had oval ends, I just can't find it to copy the block procedure, and I can't remember how I did it. Attached are the image and a block dwg.

[Ed__Jobe]

Here's one of mine that sounds similar. It's a cable wiring diagram.

[Jaycee.foli]

Not quite what I was looking for. The stretch would be directly related to the text, so that as you type in the text, the rectangle stretches itself to accommodate. Kind of like the mtext text frame, but in this case it would be a block and attribute.

[h_s_walker]

If you make the attribute a multiline attribute you can use the mtext frame, otherwise you cannot stretch anything based on the length of a string of text

[Jaycee.foli]

I made  the attribute multiline, but could only use background mask, could not use a text frame.