To me, the question is whether the ball has, as part of the normal course of play, arrived at a place where it would be perfectly normal for the player to use a body part other than the foot to play it. If it has, then that's fine. If on the other hand, the player has deliberately manufactured or contrived an artificial situation solely in order to avoid using the foot to play the ball, in order to avoid the restrictions in law 12, this is circumvention and is illegal.
Based on the examples given in the original FIFA circular # 488 that introduced the idea of circumvention, this would include such things as flicking the ball up with the feet to the knee, head, chest etc or kneeling or lying down to use the knee or head to push the ball to the keeper.
In all the scenarios given by FIFA, the ball would be in a position either on or close to the ground where the most normal instinct of a player would be to kick the ball and where it is evident to the referee that the reason for him not just doing the natural thing and kicking the ball, is to avoid the restriction on deliberately kicking the ball to the keeper.