Can i add some swiches or another joystick to the O/I controller??
yes yes you can. go download the pin out guide from IFI and that should help you figure out how to make a custom UI.
refrence guide
page 6 should be helpful to you
The Blue Alliance did an episode on custom controls. If you watch it, we explain how you can wire your own custom controls (including modifying an Easy Button!).
We also have show notes (pdf) for the episode, with schematics of how to wire up your own controls using switches and potentiometers.
Check it out, I am pretty sure it will show you exactly what you want.