HTC Incredible - always on soft button lights when screen is on
In Cyanogen ROM there are options to tweak the auto brightness levels, including the "Buttons" level. Setting it to 255 for all brightness levels should keep them on all the time. It is also possible to add or remove brightness levels.

http://chromloop.com/2011/06/how-to-optimize-the-automatic-backlight-settings-in-cyanogenmod-7/

Rooting and using a custom ROM may not be an ideal solution, but it should get the job done.