Thanks for the reply. Unfortunately this does not solve my problem.
The document generation code is flexible enough to work with every record type, so I would like to add the additional button to each one.
This just adds the button to the contact records. I could probably add all the different record types from the base install (contact, company, task, phonecall, etc.) but then it wouldn't work for new extensions.
Even getting the list of all records dynamically from the database wouldn't work as registering the processing callback is done at install time and record types created afterwards would not get the extra button.
If there is no better solution that's ok. I can patch RecordBrowser_0.php on every update. It just seems unclean,