Hy i am using APC and he has some functions that i want to integrate so nu sphere can recognize them and offer me the code hint that i love so much.

I could write some dummy code and include it into my project... but i am curios is it possible to add it without the function being in declared?

You can, but it's not easy... You have to look in the config/ folder for that. The file you want as an example is called "func.rel". It's an XML file with a list of modules/functions to use for code hinting etc.
It is possible as it says to add your own files with definitions. Unfortunately I have no idea of the format.