Im not a certified pilot but I do have flying hours in a C 185, so my answer will be to the best of my knowledge.
In the case you mentioned, shutting off both of the engines, would not be a very good idea. I would deploy the airbrakes until the drag produced by them cancels out the thrust produced by the engines. Then you would be able to control the speed by extending/retracting the airbrakes.
Once again, this reply is not from a proffesional, only an aviation fanatic and a future ATP.