You could perform the automation from Word using Word macros. The integrated Visual Basic macro language can give you programmatic control over mail merge. See the following article to give you some ideas.
Hi John, we are going to try your suggestion. Current process is they print out the letters, scan them to TRIM then post these letters but they'd rather save these letters as Word docs. Many thanks ... A
Have a good look at Bing (http://bingmail.com.au) . These guys offer a 'Print-to-Post' service which may be the final piece of the puzzle. A glorified printer driver is installed on your system which instead of printing on a printer next to you, is sent to Bing. Bing interprets the address on the page, stuffs the printout in a letter, and posts it.
Definitely worth a look.
Disclosure: I do not work for Bing but my son is on the same cricket team as a gentleman who does. We discussed the Bing service while we watched my son score 2 for 10.
Further Disclosure: The first disclosure was really an excuse to say my son took two wickets for ten runs........
Other then the content; a suggested approach is to leverage off trim to produce the mail-merge letter end to end. e.g contact details(locations), record number(emebdded to footer), PDF conversion (to email) and importantantly save each merged letter individually....although it requires coding