How To Remove the Lines and Boxes On A Form?

[ghporter]

I have a form with graphic data filled in it, and I have the blank form. I'd like to somehow use GIMP to remove the form's boxes and lines, so that ALL that's left is the graphic data. The form is printed in blue, while all the data is black.

I tried removing the blue color from a scan of the completed form, but the graphics overlay the lines, and it became a pixel-by-pixel struggle - and so error prone that I gave up.

Is there a way to use a scan of the blank form as a mask to remove the printed info from the form (lines, boxes, labels, etc.) from a completed form?

Here's an example (not precisely the same thing, but it's close) of the kind of form I'm talking about (sorry for the size of the image):

And a filled example:

Thanks in advance!