I was thinking about your original question and it sounds like something i do and Bruce is right much cunning was required, it went something like this:
1. Click on button asking for report (from browse or anywhere really)
2. This calls a NetWebPage, that is mostly just HTML saying "we are preparing your report... blah blah blah".
3. This NetWebPage contains a Javascript Interval (every few seconds) that calls an AJAX function on the server that checks for the existence of the "expected PDF filename, that is only available once the report is completed. If its not ready AJAX function say no, if it is ready AJAX function returns yes. The original NetWebPage in step 2 above knows that once the AJAX function returns yes, it can redirect you (window.location=""; or similar) to the PDF.
4. Meanwhile if you get bored and go off and do something else, the report is still produced and it sitting in your "Report In-Tray".
Works very nicely on one of my apps, and is my preferred solution to handling reports on web based systems. As some of my reports are ready within seconds and others may take minutes.
Regards
Bill