Freeradius proxy support

Hi, I'm new to Freeradius. I would like to get some pointers and documentation details about setting up Freeradius as proxy. Our requirement is to have a Radius proxy and modify the Access Accept response based on certain criteria. Few questions regarding Freeradius proxy support. Does Freeradius proxy has support for a plugin probably in Java to snoop the Radius request calls? Does Freeradius proxy setup has option to specify which Radius server to pickup based on some attribute value in Access Request? Our requirement is to have multiple Radius Servers for certain groups. This group information will be available in one of the VSA in Access Request. Any help will be really helpful. Thanks, Ila.