The approach I've decided on is rather unglamorous:

I'm going to put the long title in the autotext as a bookmark. When the app runs, if it finds a bookmark called "LongTitle" it'll copy the contents to the subject line and remove the bookmark text and all.

The real solution to many of these problems I encounter is the "document management" approach: put all templates, documents and their related autotext, bookmarks,docvars, security setting, etc. etc. in records in a SQL database. Ah, maybe the next version???