RE: jato bottles
It should be possible, but it is something that you would want to fall off or be jettisonable after takeoff. Two motors would be easier to balance, thrust-wise, but you may have a problem getting them to fire at the same time. Depending on the weight of the plane, you may need larger than a D size motor, which in the states requires a license in some areas. Look around on the Internet for the specs of model rocket motors, especially the reloadables, which are machined aluminum tubes and use the same mixture of solid propellant that is used on the space shuttle SRB's. If you would like to discuss more, Pm me, I may be able to present some ideas for jettison