I can't help you if you're attempting to do a mail-merge with the addresses. However, if you're willing to type in (or copy/paste from another source) each one, here's how:
change the "top, bottom, right, left" margins--I usually go with .3 or so, but it will tell you you're outside of the print margin, yet I have zero problems
Then, you can type in the return address and adresse's info... centering/indenting as you would like.
Hope that helps some