If you're on Windows I'd suggest trying out AutoHotKey, other users have already tackled scrolling with the Marble Mouse (I used the script a the bottom):
http://www.autohotkey.com/board/topic/4677-wheel-button-emulation-script/
Logitech's solution that comes with their drivers is strange: you click once to enable 4 way scrolling and click again to disable it. You can't hold and scroll which is what I was after. I wound up uninstalling their software.
After fiddling for quite a while, I came up with this script that works fairly well. Holding down CapsLock enters into "mouse wheel" mode. It's also possible to hold CapsLock+Ctrl to get alternate behavior (like zooming), depending on the app. The script needs to constantly reset the mouse position to keep it on-screen, so it hides the cursor for the duration of the mode (grab the cursor-hiding script as well).
CoordMode, Mouse, Screen
*CapsLock::
MouseGetPos, xposinit, yposinit
xposlast := xposinit
yposlast := yposinit
SystemCursor("Off")
SetTimer, ButtonHold, 10
KeyWait, CapsLock
SetTimer, ButtonHold, off
MouseMove, xposinit, yposinit, 0
SystemCursor("On")
Return
ButtonHold:
MouseGetPos, xpos, ypos
if (ypos > yposlast) {
MouseClick, WheelDown
} else if (ypos < yposlast) {
MouseClick, WheelUp
}
MouseMove, xposlast, yposlast, 0
Best Answer
You can use KeyRemap4MacBook:
Replace ModifierFlag::FN with VK_CONTROL for either control. Keys that aren't modifier keys can be mapped to EXTRA1:
Key Repeat > [Pointing Device] CursorMove to ScrollWheel Rate changes the scrolling speed.
See the source for the key code values and predefined settings.