Setting Access-Control-Allow-Origin in ASP.Net MVC – simplest possible method

I have a simple actionmethod, that returns some json. It runs on ajax.example.com. I need to access this from another site someothersite.com.

If I try to call it, I get the expected…:

Origin http://someothersite.com is not allowed by Access-Control-Allow-Origin.

I know of two ways to get around this: JSONP and creating a custom HttpHandler to
set the header.

Is there no simpler way?

Is it not possible for a simple action to either define a list of allowed origins – or simple allow everyone? Maybe an action filter?

Optimal would be…:

return json(mydata, JsonBehaviour.IDontCareWhoAccessesMe);