Passing side documents to stylesheet (in Java)

My XSLT stylesheet is using several side documents that are
constructed at run-time.

Back in PHP I was passing them using a stream wrapper and a custom
"arg:" protocol. Then, for example, the stylesheet could get access
through document('arg://mydoc').

Obviously, that doesn't work in Java. So how do you do it in Java? I'm
using JDK 1.5 and the standard java.xml.transform package.