[plt-scheme] Continuation handling in web-server

Hello,

I've been looking at the continuation-handling code in the web-server
collection, and I wonder if it can be used in this scenario.  I need a
web page with a flow of control like this:

     Web Page A)
       Form f)
         Button a) -> continuation to page B), which updates a value
            needed by page A)
         Button b) -> continuation to page C), which also updates a value
            needed by page A)
         Button c) -> Submits form f)

Note that this is necessarily more complex than the add.ss sample
servlet.  The user may or may not elect to invoke button a) and/or b)
before clicking on button c).

As far as I can tell, the send/suspend approach can't handle this
situation, but it is doable with a less principled use of
continuations.  Please let me know if I am missing something.  Any
other suggestions are welcome.

Thanks.