Transaction rollback and web services

Question

Given an example of calling two web services methods from a session bean, what if an exception is thrown between the calls to two methods? In the case of not calling the web services the transaction will rollback and no harm done. However, the web service will not rollback. Of course, even with a single web service there is a problem. While this is a generic question I am interested in solutions having to do with EJB session beans.

An easy and customized answer would be to add a special "rollback method" to the web service for each "real functionality" method. What I am asking for is some standardized way to do so.