custom inteface/listener

Greetings all - I wondered if any of you are familiar with how to write a
custom listener to do extra processing around the actual call to a COM
object?  My problem is that in the wsdl files that apparently came out of
the ms soap toolkit 2.0, the means of writing this interface file was more
simple (actually partially provided for you)- but I don't have 2.0, I have
3.0 and it's completely different.  So, for example, if the COM component
normally reverses a string and returns it, I'd like to (in ASP or any other
client code) overload the function to be able to call the COM component
myself and then capitalize the string before it goes back to the client -
without editing my COM dll code.

(it's a simple example, but that's the idea) I have the custom listener
file it generates for me, but that doesn't contain the overriding
interfaces for the functions.

thanks if you can help at all or point me in the right direction.

-george