Post Reqest with dictionary

Is there way to put a IDictionary to WWWForm fields?
Function “AddField” allows to set only string values. Is there way to put string like this:

{ "get": { "coin": "10"}, "give":{ "diamond": "1"} }

Thanks;

Ok, so have to put it like a data (Just example):

string params = " { \"get\": { \"coin\": \"10\"}, \"give\":{\"diamond\": \"1\"} }";
byte[] data = System.Text.Encoding.UTF8.GetBytes(params);
var www = new WWW (url, data, headers);