Sorry, it won't work.
With a terrestrial aerial the signals only pass one way along the cable, so (subject to sufficient signal strength) splitting the cable works. With a satellite cable, signals pass in both directions (with the satellite receiver sending a signal to the dish to set the correct polarity at the LNB - which is the 'sticking out bit').
You can still use a single dish to feed two separate devices but you'll need a twin (or dual) LNB attached to the dish, with a separate cable for each signal. A Sky dish may well already be equipped with a dual (or quad) LNB, as Sky+ requires two separate feeds. (One for the channel being watched and one for the channel being recorded). If not, dual LNBs are cheap (and simply screw in) but you'll need to take care to make sure you get the correct fit (as Sky use non-standard fittings).
Chris