In theory - yes it is possible, but practically - I wouldn't attempt it. Even if you were able to cut the alluminum away (not sure why you would take this route - surely the keyboard can be taken apart in some manner), you might find that the "keyswitches" aren't making contact with any actual PCB traces or such, but rather are some kind of flexible polyester plastic membrane of sorts, with the traces on this membrane (impossible to solder to, but you could use conductive glue, possibly).
Also - if you are planning on a lot of buttons - you wouldn't want to wire them up individually. Instead, you would want to hook them up in a row/column matrix - which is likely how they are hooked up to the microcontroller in the keyboard itself. Your best bet, then, would be to take the keyboard apart (this might be difficult depending on the keyboard), locate the controller, then locate the lines coming from the keyboard. There will be noticeably fewer lines than there are keyswitches, of course. From there, you would need to decode the matrix (no small feat in itself depending on how it is set up). Once you know this, then you can hook those lines into your Arduino, and be able to read them just like the original controller did.
Finally - if you need something with a lot of buttons - look into building and part for a Monome controller - plenty of projects and examples out there...