This is absolutely possible. You can work completely outside of anything JTA or EJB in Seam. To load up a local datasource, you need to use a RESOURCE_LOCAL transaction. Then configure Seam to use entity transactions. You can either use a JNDI datasource or configure one directly in persistence.xml.
Thanks for the response. Do we have any examples on this? I'm going to test it out first. Because the last time I tried using RESOURCE LOCAL transaction it doesn't succeed transacting a form in a pageflow process.