WebAPI: How to replace '_' in Request URI for JSONP callback with word 'callback' in WebAPI

The Request URI coming to my Web API contains '_' to define the callback function name

(eg. .../?_=callbackfunctionname&..).

Is there anyway to replace it with 'callback' before it reaches

Request.CreateResponse(HttpStatusCode.OK,objectname).

I am using WebApiContrib.Formatting.Jsonp . Thanks,