FFJSON半流解析

I'm newbie to Golang, and we have problem with JSON parsing. We have structure like that:

{
 method : "get",
 endpoint : "users",
 data : {
   key1 : "val1",
   key2 : "val2",
   ... 
 }
}

And out data value can be very large, so default library produce a lot of garbage during parsing. Our goal is to parse generic JSON, and send data to endpoint, so we don't need to parse it. I can not find out how to do it correct in ffjson, how should by struct be described?

type struct Entity {
   Endpoint string
   Method string
   Data ???
}