Take the Cube over to the corner with the hole in the glass and fire a portal through the hole and on the wall to your right. Take the Cube in with you and set it down on the red switch in here, doing this will cause the orange propulsion dispenser to start.
Turn to your right and wait for the gel to have just passed the ramp, now disengage the transportation beam and the gel will fall down, coating the ramp and the floor leading up to it. Go back to the Experimental Cube, pick it up, then drop it on the red switch outside.
Now walk to the start of the orange gel on the floor, line yourself up with the ramp, run forwards and you’ll catapult yourself into the beam, which will now carry you all the way over to the exit!