Won't work gselliot, due to the nature of how the digibox and the LNb inter-react.
The LNB receives in two different polarities, horizontal and vertical, plus high and lowband, making four different potential states; Vertical Low band, Vertical High band, Horizontal Low band and Horizontal High band. It can only operate one at a time and needs a command from the receiver to tell it which state to receive in, therefor, a second receiver may send conflicting requests to the LNB.
What you need is a twin or quad LNB, if it is a
Sky minidish, you can pick one up for £30 or so on
Ebay

, then all you do is run a second cable to the extra digibox.