Hope you're still reading - I highly recommend one of the third party mouse managers like SteerMouse or USB Overdrive or ControllerMate.
I found the arch of the Magic Mouse just too low and went back to the old reliable Logitech MX Revolution, but I will never install Logitech software again without an excellent reason. These packages will let you configure all of the buttons and SteerMouse (haven't verified for the other two) will definitely let you specify linear or accelerated wheel scrolling with variable degree of acceleration.
You can use KeyRemap4MacBook.
Scroll by moving the pointer while holding the secondary button:
<autogen>__PointingRelativeToScroll__ PointingButton::RIGHT</autogen>
Scroll by moving the the pointer while holding F1:
<autogen>__KeyToKey__ KeyCode::F1, KeyCode::VK_MODIFIER_EXTRA1</autogen>
<autogen>__PointingRelativeToScroll__ PointingButton::NONE, ModifierFlag::EXTRA1</autogen>
Scroll with F1 and F2:
<autogen>__KeyToKey__ KeyCode::F1, KeyCode::VK_MOUSEKEY_SCROLL_UP</autogen>
<autogen>__KeyToKey__ KeyCode::F2, KeyCode::VK_MOUSEKEY_SCROLL_DOWN</autogen>
Scroll by moving the pointer while holding the primary and secondary buttons:
<autogen>__SimultaneousKeyPresses__ PointingButton::LEFT, PointingButton::RIGHT,
KeyCode::VK_CONFIG_SYNC_KEYDOWNUP_notsave_pointing_relative_to_scroll</autogen>
See the source for the key code values and predefined settings.
Best Answer
I haven't heard of a new tool for some time, but SteerMouse might be worth a look, but it depends on your current OS version. I'd verify it would work with you machine before you download/purchase.