is the body of your document the same and only the "who"
different? if so, how about trying these options:

option 1. in winfax, modify the fax header to state
recipient's name and company and whatever else. add your
recipient to your contacts list. create a general
document in word then print to winfax, select your
recipients. each recipient would have the same document,
but the transmittal at the top of their page would read
only their info in the recipient info of the banner.

option 2. in winfax, create your document in cover page
option as a cover page. use the fields of recipents
name, etc. close cover page window. select send new
fax, select your created cover page, select your
recipients.