A quick update to this. I have now created an ID creation utility which uses a couple of reports in SIMS.net (pre-admissions and on roll), exports some XML files and then uses these to create an ID (with the template for the ID being fixed with a bmp file as the background).
It also keeps track of when an ID was printed (so, if you're doing 700 of them and only get 200 done in a day, you can see where you're up to).
It is set up to work with our Magicard Tempo printer, but if anyone else would like a copy, I will make it available and try and make it so it works with more than just our printer here.