Deirdre, A possible workaround is to create a special paragraph format and put it in the text frame on the body page. Put the variable in it as the only text. Then set the color to white to make it invisible. (You can also set a very small font size for the paragraph to reduce its effect on line spacing.) The TOC will then be able to pick up the paragraph text from the body page.
There are a couple of potential problems: 1. Being invisible, there's a chance of accidental deletion. 2. White text on a white page is invisble to the eye, but not to speech synthesizers. So if you have sight-impaired readers of your resultant PDF, they'll hear the variable text pronounced with the other text. Mike Wickham