Set yourself up to fling through the fizzler, and then do it.
Put two portals to catch the pellet and redirect it into the other corner. Then quickly enter the corner and put portals in to make it go in the receiver.
Put your portal on the white wall above the entrance and then take the side path. Fling yourself from that ditch, but while midair, place your second portal on the ground to go even faster and through the fizzler.
Fling over the next fizzler and set portals up to send the pellet into the receiver, then fling back over.
Progress on the platforms by shooting a portal further down the tunnel and jumping onto the next platform. Keep doing this until you reach the end.
Get portals behind the buttons of both rooms and push them both in quick succession. While the doors are open, quickly use portals to shoot the pellet into the receiver.