Like MG said, he will eventually learn to find the dummy himself. I used to leave a couple in the cot for Nina, and if she woke during the night, she search for it and would always find one. She was about 6 months old at that stage.
What he's doing could be out of habit. It should be relatively easy to get him out of the habit as he's still so young. They say do the same thing for 3-5 nights, and if nothing has changed, stop and try again, or try something different in a few days time.