Add a defender behind the cutter: A must keep in mind the speed of the cutter so that the throw is delivered to R before B arrives; if the disc arrives too late then - were a defender present - the defender might be able to get a block
Player A should try to put a bit of a curve on the disc to slow it down when it reaches R, rather than trying to perfectly time their throw
These cuts should mirror those used in your offence; some teams prefer to take a few steps to the open side before cutting to the break side (making it easier to break the mark), or to take a few steps away before turning under (to mimic a cutter coming back towards the disc)
Once the throw is complete, the cutter cycles around to the back of the other stack, and the person who just acted as the mark becomes the next thrower in the queue. Meanwhile, whoever just threw the break mark throw now cuts for the other stack.