I dont know what controlers you are using but let me suggest something. I have allways assigned 'Ctrl' to a button on my throttle and 'Shift' to a button on my Joy. So lets say you have four buttons on your throttle hat. You will now have eight commands. You have the normal commands and then four 'plus shift' commands. Same goes for the joystick ect.
Try it out, it will double or maybe even triple the amount of buttons you can have.
I have also used a USB numeric pad. Its an easy add on.