I've put together a document that does the calculations required for cross-platform vertical metrics. The calculations are based on the methods described by John Hudson in this thread: http://typophile.com/node/13081
This document was put together in iWork 09 Numbers and I've exported an Excel version so hopefully all the (simple) calculations have survived intact. Also thanks/apologies to Karsten Lücke who’s diagram I have ‘borrowed’ and butchered for my own needs. The document contains two methods: John Hudson’s original method (under ‘Best Practices’ in the previously linked article) and the revised method suggested by Read Roberts (under ‘Update’ in the article). As far as I understand the jury is still out on which method it is best to use. Default values in the document are all taken from John’s original article and all values are positive so you should manually change them to negative figures when inputting them into FontLab.
Comments, suggestions and reworks are welcome!
EDIT: The forum won't allow .zip or .numbers attachments so I have attached the Numbers version as a .txt file. You should be able to download it and change the suffix to .numbers to successfully open the file in iWork.