Is there an effective way to map a mouse's thumb buttons to alt-left and alt-forward?

I've been trying the imwheel route using an MS USB Wireless Intellimouse Explorer on a new 9.1 installation. (Seven buttons on this mouse: left, right, two for the wheel, and two thumbs buttons on the left side.) It isn't working. After making the appropriate XF86Config edits and issuing the usual xmodmap and imwheel incantations, alt-left and alt- right are mapped to the wheel. That's despite the fact that I tell imwheel to map to buttons 6 and 7, which, after the xmodmap, xev indicates are the thumb buttons. In other words, prior to xmodmap, imwheel sees no button 6 or 7; after xmodmap, xev shows the thumb buttons as 6 and 7; but imwheel "67" does the mapping to the wheel. ("Buttons 7" and "ZAxisMapping 6 7" are in XF86Config.) Plus, the wheel stops scrolling. With "ZAxisMapping 4 5" in XF86Config and without using xmodmap and imwheel, the scroll wheel works.

I've managed to do this on other distributions, but have always found imwheel to be more trouble that it is worth.

Is there a better way?

A better way might be a new mouse, too. Anyone care to recommend a mouse that "just works" or comes with Linux software/drive that takes care of the mapping issue. Doesn't need to be wireless or USB.