I'm half tempted to have a go at this, if I get a decent lucid soon (not very frequent at the moment). Personally I would raise my hand into my view like you see on Skyrim (first person) expecting to see the flame, then draw my hand down like happens when you hold the button for casting, then release. I've used "Fus Ro Dah" before and it worked, I saw an energy field leave me and go foward, the effect was weak though, perhaps the strength of just "Fus Ro".

With all the games I play though I really can see casting spells as a useful tool which is why I'm wanting to try it when I get a chance.