Hand belt sander for uneven surfaces

Standard hand belt sanders work well for taking an even amount of material from an even surface. But for taking an even amount of material from a slightly un-even surface, they don't: they even the surface first, which results in a loss of a gentle unevenness that adds character to the surface. This could be solved with a set of additional independently-moving spring-loaded rollers pushing the belt onto the surface. The greater the number of rollers, the more un-even the surface can be. The diagrams below illustrate: