Chris and Ally,
I still suspect there is at least a work around for this, though I remain unclear about what exactly you need.... maybe I was not clear in my question above. It sounds like some letters are to be signed-off and some are not; both by the same sender, correct?
If so, that person will have to make the choice as to whether sign off is needed or not, when they compose it, right?
And we are talking about letters composed in the letter writer, correct?