While I've never used a Bamboo, the button on the pen is like the button on a mouse for extra functions - not to actually "use" for normal activation - like it replaces a middle and right button - not the left button.

I'm gonna guess there's no way, but what you may be looking for are in the brush settings - in Photoshop, get a brush (hit the letter B), then hit F5 and all your controls are in there - click on individual tabs and adjust their parameters - don't be afraid to play all over the place - if you don't like what you've done, click another brush and it gets rid of all the info you just changed.

If you LIKE it and wanna SAVE it, click the little right-arrow at the top right corner of the dialog box and one of the text menu options is something like "Save New Brush Preset" - click it, name it, and have fun playing with it again and again!

I hope this helps - good luck and happy painting-

-Lew ;-)