Yes, there is another way. I do this all the time, works great. Download the JBoss AS source and compile using JDK 5.0. You will get two JBoss AS builds in the build/output directory, one the standard build, the other for ejb3 (they are clearly labelled). Deploy the portal to the ejb3 build.
Oops, I didn't see that you also want RC9. In that case, do what I described but download the JBoss AS 4.0.5 source code.