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.