I have a extra joystick laying around. I really only used it for star seige, and am willing to sacrifice it in order to make a clutch pedal since my DFP doesn't have one.
I'm thinking modifying it a bit with a flat plate so my foot rests at the base and pushing forward would just be assigned to the clutch.
It'd be much easier to find a spare old steering wheel and use those pedals instead. Or you could use the joystick as a handbrake/gearshift. But if you're good with your hands, go for it.
I'm really cheap so that is the exact way I did it. Another way you can improve the feel and driveablity of LFS is to get an old Mad Katz wheel and use that Gran Turismo 1 shifter on the side, not too far off the DFP's size and action and rig that as a hand brake for autocross/gymkana and drifting. Sure makes things alot more fun having controls similar to a real car!
+ a million on a spare set of pedals next to the existing ones.
I don't know if it's a good idea or not, but it is possible. Below are pics of what I used with my DFP before I got a G25 (sooo much better:nod. The pedal and base were from an old thrustmaster wheel/pedal set. It had been dismantled and broken and used for other stuff I can't remember, so I couldn't use the old pedals for the clutch.
The joystick had some old connector, so I somehow just used the joystick mechanical parts to move the electronic bits from the old steering wheel, which was usb. I really don't remember what I did and I don't want to take it apart right now.
You wouldn't have to do any of that if your joystick works already, but a base is a good idea. You might also want to put something flat on the joystick so it actually feels like a pedal.