This can be done in Chapter 3. The Gamma spot is at 23,10.
Go to 27,11 and climb the wall. Go all the way to the top, where the blue power up is. Stand in front of it and drop down from the ledge and grab the power up. Now quickly use it (L1). Make sure you look to the left, since this will shoot you horizontally towards where you’re looking. Grab the ledge again and follow the path. You’ll see a yellow power up. Grab it and use it to shoot yourself vertically up in the air. When you’re almost at the top, deactivate the power up (L1) and drop down the narrow path below you. Now follow the path and grab the ledge, above the red power up. Now let go of the ledge, grab the red power up and when you’re about to fall towards the room below, use the power up for a super jump and aim toward the next wall. Now grab the wall, above the green power up. Now turn into a ball (X) and use your speed boost (R1). You’ll grab the power up while falling down. You’ll want to hit the floor of the room below first and aim towards the room next to it, on the left. In this room, hit the floor once more and while at the point where you’re about to go down again, activate your power up and you’ll be able to fly wherever you want. Be careful, hit anything and the power up will deactivate itself. You’ll see the Gamma icon on your left.
Credit to: http://www.ps3trophies.org/game/knytt-underground/guide/
Credit to Mr Vuule for the video