If you can't get close enough in the mornings without busting them off the roost, then try this, it has worked for me more than once.
Go in after they go up to roost in the evening from the opposite way you have been going in during the mornings. Walk and make a lot of noise and bust them off the roost. Hopefully the gobbler will fly back towards the way you have been coming in during the mornings. If so, he should be easier to call to you since he will be sleeping without his lady friends.
Make sure though that if you are going to do this that you wait until it is good and dark. If it is still light and they spook from their roost, they can still see better once they take flight above the tree tops than you can see from the ground and if it is still light enough for them to see they could all fly the same direction. What you are wanting to do is make them spread out, that way the gobbler is hopefully separated from the hens..As soon as it gets light, the ole boy will be anxious to find a girl again. That could be your ticket.....