If there's a car already past you, there's no way to "give way" to it anyway.
If there's a car on the opposite side of the roundabout, unless you're a real slowpoke you'll be out of his way by the time he gets to you.
If the car on the roundabout approaching you has his left indicator on, he's going to exit the roundabout on your road so he's not stopping you. (Obviously keep watching him in case he's indicating incorrectly).
So the only cars you have to wait for are those on the roundabout with either no indicator or right indicator on, approaching you from the right, where there's not enough room for you to safely go in front of them.