Can a ClientCallback be Synchronous?

[GroupReader]

I'm trying to implement a Client Callback in ASP.Net 2.0, but I need it
to be synchronous, not asynchronous. There's a parameter on
ClientScript.GetCallbackEventReference called "useAsync". First, the
name of the variable does not match the documentation description.
Second, I've tried both true and false for this value, but the code
always executes asynchronously.

In javascript, I need to update the value of a string using a client
callback, then do something with that string variable. The problem is
that the javascript code continues on before the call to the server
function has completed and "does something" with my variable before it
has been updated.

Any help would be greatly appreciated.

Thanks!