I am currently designing a custom mailing list webapp for a client.  Is it possible to run a background process through a servlet on a shared hosting account?

It seems that most of the frameworks that would make this possible aren't allowed on shared hosting.  I would like the mailing process to run on a background thread so it isn't reliant on and doesn't stall the browser (esp since jobs could take 2-5 hours to run).

I'd rather not have to make the client have a stand-alone app for it.  Any ideas, suggestions, or advice would be very much appreciated.