Depending on what you're trying to do you could write a small java WS client which would print your metrics out to standout. At that point it's (relatively) easy to create a Hyperic friendly wsmetrics-plugin.xml which would then behave like any other HQ Agent metrics gathering entity.
if not a java client, there is a really nice perl web services package which makes it really easy to make a client.
The Hyperic Documentation has many examples on how to create a scripted plugin. All you have to do is create the script. Pick your favorite language, I only say perl or java because i've done this in the past.
good luck
