How to add text block to a submodel

I'm trying to figure out how to add data to a submodel diagram programmatically.

By 'data' I mean ancillary information solely for the benefit of people looking at the diagram. 

The most obvious way would seem to be to add a Text Block but I can't figure out how (programmatically) and this thread makes me think it's not possible.

But I don't really care (within reason) what it takes to get something to appear.  Ideally, I'd like to put a small bit of text (10 char max) near every entity/table on the diagram.

Is such a thing possible??
If so, how