In the print dialog, adjust the layout for the Sender; changing the height is easiest. You’ll need to create a custom layout for this first. Also, you cannot change the size indefinitely (try blowing it up to huge proportions and you’ll only get extra white space). Note that I’ve never really used this before, but I got curious about it though, so tried it. I did run into some problem with the fields being non-editable at first, but after closing the print dialog, then opening it again (with the new custom layout selected), I could change the values. Might be a bug (OS X 10.4.11). Just in case. Hope that works for you.