Advanced options for inserting fields on drawing formats

I've created a drawing format for our company and I want to do the following:
Our file names start with a unique number for each file on the server. Now I want this number to show up in the bottom right corner of my drawing format.

I can use insert field for that in a note text box. But it only let's me select the entire file name. This file name also contains a description and a revision number. They're separated by underscores [ _ ]. Is there an option of telling Spaceclaim to only insert part of the file name, let's say only the first 10 characters or the last 4, or the ones between the underscores?

If such an option exists, I can let the drawing format load the necessary info from the filename. Now, all my colleagues have to do it manually. If someone forgets to type or correct the revision number, the drawing is screwed up.

Hopefully someone can help me out on this. Otherwise it might be a nice enhancement for SpaceClaim.