Hivetranse: How to configure transaction demarcation for existing datasource?

[Aleksej]

Hivetranse quick start describes only how to create datasource for 
application,
but it is not an option in my case ( more than one webapp uses the same 
DB ).
For Hibernate I just specified Tomcat's datasource in hibernate config, 
but how
to do the same think for simple JDBC transaction?