@Borrelnoot
You might consider that tool:
http://wiki.github.com/rvalyi/ooor/howto-connect-ooor-to-multiple-openerp-instance-easy-data-migration
More generic API explanations here:
http://github.com/rvalyi/ooor
Also, this now works inside the Kettle ETL:
http://github.com/rvalyi/terminatooor
Even if we are yet to make some user documentation for that last one.
Now of course there are other ways too (python coding, database shared funding may be...).
Hope this helps.
_________________
Raphaƫl Valyi
CEO and OpenERP consultant at
http://www.akretion.com