I've never needed to. It works really well the way it was taught. When people see that there is nothing written and it's just blood under the skin, they go nuts.
Well there was a tip offered by Banachek in his Psi Series to make the mark not visible prematurely which is by raising your arm a little higher so all the blood flows down and reveal appears when you lower your hand letting the blood flow down the arm.
If my explanation wasn't clear I suggest you check out the DVD's from Banachek.
200% agree, don't push the limits when it's not even necessary.
Consider they don't have to "see" that there's nothing on your arm, you have just to make remember that there wasn't even a reason to suspect to look at the arm.
Hope it helped