Foot pedals as modifier keys for Mac

I am hoping to buy a couple of foot pedals that I could use as Ctrl and Shift for my MacBook Pro. Is this at all possible with an OS X machine? I have read that Kinesis foot pedals (e.g. this one) cannot be used as modifiers in combination with other keyboards. Is this correct? If so, why?

I created my own "keyboard combiner". It lets me use the Kinesis Savant Elite Triple Foot Pedals for shift, alt, and command modifiers on a Mac.

https://github.com/davidbkemp/KeyboardCombinerArduinoSketch/wiki

It is quite easy to assemble, but I cannot guarantee that it will work for you. It certainly does not work with some pedals and some keyboards. For the Kinesis pedals, you will initially need to configure them to act as shift, alt, and command keys, and that means using a PC to do the initial configuration.

Definitely possible, there's this great ControllerMate software that lets you assign keys and keyboard shortcuts to various pedals. Take a look at the following SuperUser answer: https://superuser.com/a/1486751