Printing mailing seals on Xerox WorkCenter 7345 PS???

I am trying to print a color text on small round transparent mailing seals (1" diameter). I have a Xerox WorkCenter 7345 PS. When I feed it through the tray 5 (byp) it will not take it in saying it needs to be a heavy paper (I had to choose 'postcard' option since that is the size of the sheet). Obviously, this is not a heavy weight paper; it's labels. Do you have any suggestions on how to best print these small round labels?