Model car initial thrust director idea-design help?

[festinoracing]

Okay i am entering a competition to design a model f1 car that is 30cms long it is owered by a co2 canister in the back of the car. High speed camera footage of the gas bing released from the cartrage indicates that some extra gas is bein lost on the initial thrust. i was thinking if i placed a gas director on the lancher that it would be able to push the gas back out giving the car some extra initial thrust. the car must travel 25metres there are no turns in the track. any help on the shape of the director?? any background into why it will work? or if it will even work? i have included a video of a team that have done it before at 0.20 in the video link it shows the idea and at 0.24 it shows the idea in action Link
Any help will be greatly appreciated!
regards
Eamon