X-Mouse Button Control does it
A bit late reply but I hope it helps someone experiencing this problem.
There is an excellent utility called X-Mouse Button Control that allows you to specify all imaginable mouse mappings.
I just purchased Microsoft Bluetooth Notebook 5000 mouse in a hope that MS mouse software would allow me to remap middle wheel button and wheel up and down for mouse-based magnify zoom in and out, but no, IntelliPoint 8.2 does not even recognize this mouse as a Microsoft mouse (nor does the later Mouse and Keyboard Center from MS)!
But with X-Mouse, I can specify first that the wheel button triggers a secondary scheme ("layout 2"), where wheel up is configured to send virtual keys {LWIN}{NUM+}, and wheel down virtual keys {LWIN}{NUM-}, while the wheel button is being pressed down (even the delay can be set). Having the specification in a secondary layout retains wheel up and down doing their default operations in all other times than when the wheel button is being pressed down.
The utility also allows application specific mappings, and it is free. You just need to have a wheel button mouse, or a 4-button mouse, to achieve this functionality.
I tested this on Windows 7 Ultimate X64 and also Windows 8 Pro, with the above mentioned Microsoft mouse, and Dell Bluetooth 5 Button Travel Mini Optical Mouse.