Some more fiddling will be required though as I need to refer to the JARs in the local Maven repo when specifying the "code bases" in the policy file. My current set-up is hard-wired.

The need to create the policy file is of course a bummer. I guess the location of the local repo you can get from a Maven variable. Maybe you can create then the policy file automatically prior to the surefire run. You could use Java, but maybe some Groovy script is easier. You should have all at hand which you need and we already use it in other contexts.