There is no real player in FPSC as such just a Camera and control of movement for that is very limited.
You can affect its gravity - search for the jetpack and study how gravity is affected in that script.
However ther all kinds of difficulties in applying gravity or lack of it to the player (camera) and such make the kinds of player movement control you seek difficult to achieve without other side effects relating to collision and other things due to Physics and so forth.
There just isnt enough default support for cameras or player movement to make working with attempts really successful as far as I am aware.
Perhaps we will see some futher update to the flexibility of user control for the player as time go on in FPSC updates which will help along these lines. I am sure that will be considered along with many other improvements.
