You are correct. The clue of discernment is a tool for the consciousness, one that will only work if we ourselves learn how to pay attention. It is like a hammer, saw or ruler; these are only useful in building a house when we know how to use them, when we have the proper intention and application. These tools, without knowledge of their proper application, are quite useless. The same applies to the clue of discernment without an active consciousness.
I cannot recount how many times I have pulled my finger or jumped in the air to fly only to continue within the dream state, waking up in the morning having lost wonderful opportunities for investigation. I heard a story from another Gnostic instructor about this that is actually quite funny (and quite embarrassing for him). He practiced the clue of discernment by pulling his nose out like Pinocchio, and yet he did not realize he was in the astral plane!
What this illustrates for us is that discernment is a quality of the consciousness that we need to develop, and that the clues of discernment provided by the Master Samael are in order to aid the consciousness that is actively paying attention. Otherwise the tool remains what it is: a mechanical device. If we continue to be mechanical in our perception, habits and identity, then we will not know the difference between waking and dreaming life.
However, when you know how to consciously question your surroundings with the intention of discerning your environment, then the clues given by Samael Aun Weor are extremely effective. Jumping in the air to float, pulling your finger to see it stretch, or pushing your fingers through a window of glass, become indicators or means of verifying your conscious discrimination of your surroundings.
If you have the right intention, then the techniques will work. If the consciousness does not have enough strength to discern reality (since it borders between Pistis and Dianoia) then it will continue to dream, even with the best spiritual tools available.
Joyful in hope, suffering in tribulation, be thou constant in thy prayer.
Benedictis, qui venit in nomine Domini. Osanna in excelsis.
"Blessed is he who comes in the name of the Lord. Hosanna in the highest!"