Players are permitted to block each other off the ball, and some otherwise illegal techniques are legal when the ball is loose. As you point out, holding is one, block in the back is another (9.3.5A), provided these are done to separate an opponent from the ball.
Not everything goes, however. You can't spear an opponent off the ball, for example, and I would put clipping in this category. A good rule of thumb would be: if the penalty is 15 yards (PF, IBB, IHC, etc.), going for a loose ball does not excuse the foul.
I know of nothing written to support this interpretation.