There is a separate entrance to the Park-you will go through the Rainforest merch shop to access it.
To access Rainforest you will already have gone through Security,so when the Park opens you can immediately go to the Rainforest turnstile.
Hardly anyone uses the Rainforest turnstile and several times we have actually been let it the Park a few minutes ahead of the Main Gate.
Here are some pictures I took one trip showing the Main Gate line and then the "line" we encountered at the Rainforest turnstile and finally a picture looking at the Main Gate line from INSIDE the Park as we had been let in BEFORE the Main Gate.