And you'll probably only need half the liquid or it might be quite thin but as you don't normally add that much to those mixes anyway I'm not sure how that'd work. I'd guess about half a pint should do it.
Do you know you can get Shwartz slow cooker mixes? There are 4 flavours and were only available in Morrison's before Xmas but I'm sure they'll roll out to the rest of the supermarkets eventually. x