Worker Process Per HTTP Session

I have a new web service exposing a very virtual memory intensive service.
I'm using IIS 7.0. Based on the virtual memory requirements, I cannot have
more than a couple of sessions open before topping the 2GB virtual memory OS
limitation per process, because all sessions are running through the same
worker process. How can I configure IIS (e.g., web garden, application pool)
so that each web service session gets it's own worker process?

Thanks for any help