It might be easier to buy them, and the shop bought ones might well be prettier, but yours will be *healthier* and *tastier* than anything you can buy (and making them is a laugh too ...)
Are you making them red or green?
Cous cous is free on a green day. It's 1½ syns per 28g (cooked weight) on an original day.
Sausage meat will be ½syn per sausage on an original day but 4 syns per sausage on a green day.
I would say do them as original, cos you'll have more sausage meat than couscous, I'd imagine! Then weigh out your couscous once it's cooked and shared between all the eggs, it'll probably go a long way and be virtually no syns.
Hellie
ps: And if you use the Morrisons Eat Smart pork sausages, they are syn free on original, which would make your scotch eggs even lower synned
If on EE just count the syns from your WW sausages, or go with Hellie's advice and get Morrisons free sausages for a totally free treat. Let us know how you get on, they sound yum!