List of variables useable in SAM HTTP monitor?

I'd like to be able to customize the URL being checked by an HTTP monitor further than simply http://${IP}:${PORT}

For example, if I could do http://${NodeName}.custom.url:${PORT} or something similar, that would be ideal.  Is there a list of variables that can be used in these monitors?  I've gone through the SAM Admin guide, but those variables are for the Alerts, and don't match the two examples I have from the default template.