As is well known, the Java Control Panel no longer allows you to set the run time parameters. (Actually, it lets you try, but it promptly forgets them.) However, if you add the following line to the deployment.properties file (under $HOME/ApplicationData/Sun etc), then the properties are sticky and show up in the control panel:
deployment.javaws.jre.0.args=-Xdebug -Djava.compiler=NONE -Xnoagent -Xdebug-Xrunjdwp\:transport\=dt_socket,server\=y,address\=8000,suspend\=n
but I still can't attach to my applet.