Zen reports - Using the <call> element with parameters, but calling a method

Greetings!

I'm new to Zen reports and I'm wondering if what I'm trying to do is possible.  I have a classmethod  that accepts three parameters to generate an xml file from a global.    I've set up my Report Definition to call the ClassMethod that generates the .xml file; however, I'm trying to figure out how to pass the parameters to that ClassMethod from the Report Definition.  The example in the documentation shows parameter passing using SQL (which I'm not using), so I'm curious if this will work.  

Secondly, I'm invoking the zen report from a web browser, so I would need to pass the values collected on the web page as the parameters to the classmethod.  I can send the parameters when creating the URI, but is there a way via zen reports to pull the parameters from the URI so that they can be used when calling the classmethod?  Nothing jumped out at me when reviewing the documentation, but I easily could've missed it.

Thanks in advance for any help!

Brian