Send a postcard to someone using the most negligible address.
I sent the below postcard to Sir Alex Horne. When in the queue at his book signing in Chesham (thanks again to @carlalouiseee for the reconstruction photo), I turned to the person behind me and handing them the postcard said,
“Please could you give this to Sir Alex Horne?”
And they did. It had not one letter of address on it and not a jot of a stamp.