There is no clean way to pass the -javaagent parameter to the java command invocation with play 2.0.1-2.0.4 without modifying a script.
I was able to get a javaagent working using the following technique:
# Modify the play/framework/build script to include an extra environment variable
sed -i 's/^java\( \${PLAY_OPTS}\)\?/java ${PLAY_OPTS}/' ${playPath}/framework/build
Then it is possible to pass the -javaagent param like this:
export PLAY_OPTS='-javaagent:/lib/newrelic/newrelic.jar'
${playPath}/play -Dconfig.file=conf/prod.conf -Dlogger.file=conf/prod-logger.xml start
Update
An unfortunate sidenote- I just found out from New-Relic support that New-Relic definitely does not support play-framework 2.x right now (2012-10-04).