That is a very different requirement than what we have. Maybe Gimmy has a similar requirement as you and it may work for him. I would definitely perform load testing prior to going live.
We have a POS application where the user is waiting for the documents to get created and then printing them locally. No documents, no transaction. If all we did was create and store them it might be a solution. We were trying not to have to deploy the PB runtime on every client. That's why we tried the web service route but it won't be a solution for us.