I have never coded default values into my DLL, so to avoid giving inaccurate advice I cannot say much about it. It is covered in section 2.4 of the ADK documentation. It appears that default values can only be applied to float arguments, not arrays or strings.
If your arguments are floats, select a default value that would indicate to your function that nothing was passed.
My original comment about having multiple functions would look like this (different functions depending on the number of arguments):
myfunction3(myentry1, myentry2, myentry3);
Or for a superset:
myfunction(myentry1, myentry2, myentry3);
You would send dummy arguments to the ones you are not using, letting your function know to disregard them.
myfunction(numArgs, myentry1, myentry2, myentry3);
Where numArgs tells your function how many arguments to use. You would still need to send dummy arguments in the unused entries.