Merge question for Albert Kallal

Albert -
We are in the moving business and for each customer we store an "Origin
address" and a "Destination address".
There's no problem with most of the documents we produce as they go
consistently to one address or the other, so I have loaded the appropriate
mergefields into my templates and Super Easy Word Merge does the job
beautifully.
For a couple of docs however they may sometimes need to go to origin and
sometimes to dest.
When the user is producing those particular docs they will know which
address they need to use. But how can I give them the choice of which one to
pull and merge, as part of the merge process?
I thought about putting some kind of flag on the appropriate address block
on the form such as "mailing address" but that doesn't resolve how I would
have two sets of mergefields in my template and how the required one would be
selected.
Hope you may be able to help me with this...
Many thanks
CW