I like Chu's bumper, but I needed to mount it at a right angle on a small omniwheel robot. The center hole is covered by the shield socket, but I left it there anyway. You could use it to mount with a flat head bolt before installing the board, for example. However, in my case, I'm using the two end holes which are spaced to fit a (so far unpublished) robot base.
The bolt holes are deliberately a little small so a bolt will bite into it (almost self tapping) although I suggest using a nut on the other side. You could also use zip ties or double stick tape. In fact, the foot is broad enough that you can just sit it down on the bench and it will stand.
If your printer isn't great at holes, you can always use a drill bit to ream them out or drill them up to the right size.