At the top of this page I mentioned that all you had to do was make the portal longer, I made it about 5 blocks long and it ported through. However, the momentum doesn't really stay even if you use momentum keeping unless you link it high above ground - if you link it close to the ground it might skid a few meters at best since it fires in a downward arc that starts off relatively flat.
Basically as I mentioned above, it's not very efficient for transdimensional fire, but it'll look cool while you do it.