Yippee, I think this can be done. I was having a very similar problem
inserting a third line into a set of labels. Try going to "Tools" and under
"letters and mailings" click on "view mail merge tool bar." Then, where you
would normally insert the address block, click in the document, then click on
the "insert merge fields" button _on the mail merge toolbar__. When this
brings up a window, make sure to select "address fields" instead of "database
fields" at the top. Then select the first field used in your address block
and click insert. Then move the pointer in the document to where you want the
second field and repeat the process, continuing until you've created a
customized address block. When doing labels, I then had to click on "update
all labels." When you have finished, make sure to click on "Merge to new
document" in the tool bar.