I've written a vi plugin that adds autocompletion functionality for baan scripts. It does require a little bit of preparation though.
The script and installation instructions are available from vim.org. (
http://www.vim.org/scripts/script.php?script_id=3754) or more detailed on github (
https://github.com/mfussenegger/baancomplete)
Don't get scared by the early 0.2 version. It is very usable already.
The API file generation was build with LN in mind and is untested for BaanIV or 5.
I hope some of you might find it useful. And if you have any suggestions or issues just let me know.
Regards