[LAU] second mouse as HID in pd/linux

Hi all, Crossposting this to the pure data mailing list and linux audio users as it concerns PD and the linux OS also. I'd like to be able to use a second mouse as an input device for controlling synthesis in Pure Data. (Well, actually, it's a trackball I'd like to use - much more fun, but I believe equivalent as far as the computer is concerned.) However, I am not aware of a way to connect a second mouse without the operating system treating it the same as the first mouse - i.e., having it control the cursor. The first, obvious disadvantage of this state of affairs is that my cursor would then be flying around the screen and probably clicking on all manner of disruptive, destructive things whenever I use the controller. The second, possibly more serious, disadvantage is that I believe the input would then be limited to the dimensions of the screen. For what I'd like to do, it's essential that I be able to continue to move infinitely in any direction, without being limited to the dimensions of an arbitrary frame. Is there a way to achieve this without the problems above? In other words, is it possible to get linux/X to ignore the mouse, and for PD to get the movement data straight from the device? (Is this a job for [hid]?) Any advice on either front would be appreciated. I am asking now as I would like to be certain that this is possible before I shell out £30 or so on the trackball. Thanks, all! James P.S. Bonus question: At some point in the future, I'd also like to attempt something similar with a second keyboard. If anyone can answer the question identical to the one above except with the work 'keyboard' substituted in for the word 'mouse', I'd be grateful for that too.