Here are the variables you need...
recipient
subject
body
cc
...you could use these titles as your variable names so a typical message, with all the normal details, would be formatted like...
on(release){
getURL("mailto:"+recipient+"?cc="+cc+"&subject="+subject+"&body="+body);
}
P.S. I mistyped something in the first mail - make sure your first addition to the recipient starts with a "?" not a "&" as I said before - hey, I just woke up and haven't hit the coffee yet ;-) ).