Place a ladder on the bed rock layer so that only the last layer of bed rock is above it (the ceiling). throw and enderpearl just above the ladder and once you get glitched keep pressing forward until you pop out onto the ceiling.

Part 2 of the glitch. Place 4 dirt blocks and place 4 dark oak trees on then. Speed growth by using bonemeal. Once thats done break the bottome two rows of wood and plant for dark oak sapplings and speed growth with bone meal. once leaves pop up break the leaves to get through to the wood. Breaking the wood will reveal where the tree grew through the bed rock.

Below is a link to where me and an friend demonstrated the glitch:

http://youtu.be/UgZkyjQEwIQ