If the pre-numbered labels could have qr codes, that would go right to where someone who finds the book could journal from there smart phone.
Having done some more research and experimenting, the method on this page for "InsertPicture" will work, although it's a bit fiddly;http://hubpages.com/---/IncludePicture
You would create a MS Word "mail merge" label template, and in the datasource, define a field reference for "BCID Number", entering in your pre-number BCIDs into it, and adding this to the initial label in the template. along with any other text etc., in the required place, leaving space for the QR code image too.
Then following the method on the link above, you'd then need to add in the code for the QR image to the initial label in the template.
Once the initial label is complete, you replicate this to the other labels on the sheet, so all are ready to receive the merged data.
Now, essentially, once that's done, you'd never need to do it again, and the only "work" you'd need to do every time is the next bit;
For each BCID / QR code you want to create, you'd have to go to a site like http://zxing.appspot.com/generator/, generate the QR code for your journal URL, (like http://www.bookcrossing.com/123-4567890), then save the QR Code image to a local folder on your PC, using the BCID number as the file name, following the instructions in the tutorial.
So, again, it's certainly feasible from a Word point of view; it's just the time it takes to "create" the codes, right-click and save them, then run the merge.
If you or anyone is interested in this, I'd be happy to upload the examples I've created to my site for download?
MS Word label templates and more...http://www.bookcrossing.com/---/JamesUK/http://feeds.feedburner.com/bc_at_fcmp