It's would be nice if OpenTK.Input will support this. There is a cross platform besed on c++ that is called Object Oriented Input System(OIS). I know basicly how to use joystick vibration on DirectInput(using effect), but it's both based on DirectX and not cross platform. Joistick vibration is one of the things that makes game much more fun(why modern games don't use it today? :-) ).
So can you please do it?