Malcolm,
This sounds similar to something I worked on recently. I have a statement graphic consisting of a paragraph and a signature. I wanted producers to be able to change the size of the font easily from within our newsroom production software. I used a global list of the font IDs to create font tags, but then hit the wordwrap problem---in the larger font styles, text extended out of frame to the right.
I also wanted producers to have the option of adding a headshot to the statement, further complicating the issue.
I decided to use the x-position and an imagined right margin of 1190. 
At the very largest font size, it got a little less reliable, but a statement in a 102 line font isn't more than a word or two...Nun-uh...Uh-hunh.
James.
#XPression