Registering function WITHOUT it appearing in the expression builder
 

Is there any way to use the Excel4 or COM interfaces to register a function
in an XLL without it appearing in the list from the expression builder?

I need to be able do some processing in a macro called from OnTime, but
OnTime pops up a message box at the appointed time complaining that it can't
find the macro 'CALL(a,b,c)' if I use a CALL expression. Registered
functions and VBA functions in a module work okay, but I don't want the user
to be able to see this function.

Thanks,
Aaron Queenan.