Thank you everyone for sharing your code with me.  There were quite a few excellent submissions and I learned a few things.  Here are the top entries I received so far for the challenge.  I'll add to this list if any more come in that I feel are worth mention.

crms -at- sima.com is an Elite ASP.NET hacker and submitted this solution:
     http://weblogs.asp.net/dannychen/articles/439435.aspx

Raj Kaimal is an Elite ASP.NET hacker and submitted this solution:
     http://weblogs.asp.net/dannychen/articles/439436.aspx
     Raj also gets extra credit for coming up with a sample page using async tasks to demo his control.

Both of these are very fine solutions, but not quite perfect.  Most critically, both run into an issue that I don't know if it can even be worked around.  Intermittently, ASP.NET throws an error:

Session state has created a session id, but cannot save it because the response was already flushed by the application.

I talked with some dev's about this and they seem to think it's pretty cut-and-dry.  Using Response.Flush pretty much causes this and can't really be worked around.  And this can't really be done without Response.Flush.

Secondly, both are hardcoded to display a fixed message.  It would be really nice if they were Templated instead to give the users flexibility in the display.  This is a trivial amount of work, however...

None-the-less, I learned that this was indeed possible and in-fact, not that hard to do.  Hopefully someone else will be able to benefit from these examples.