Hi,
first of all you have to think about if this is really useful!
What happens if the function is missing? Why to develope a control if you have to insert a function into each pare you want to use the control?
Maybe you have to insert the function into your UserControl?
But if you still want to do:
See about System.Reflection! I have written some class to set public variables in my page and I'll think, methods can be called with this feature too.
System.Reflection.MethodInfo mi = Page.GetType().GetMethod("YourMethod");
mi.[doSomething]
Regards, Stefan