In the Mailings > Envelopes dialog, leave the mailing address box blank, keep just the return address, and click the Add to Document button. You'll get a document with the envelope on the first page -- with just the return address -- and a blank second page
of letter size. The envelope is numbered as page 0.
Click File > Print. Type the number 0 in the Pages box (which changes the box above it to "Custom Print"), set the number of copies, and click the Print button.
If your printer can hold 200 envelopes and feed them reliably, you can print 200 at one go. Otherwise you might need to do 50 or 100 at a time.
If this is something you do often, save the document to a file so you can just open it and print it.
