I would position them relatively to the background.
Right click - background - set position to mousex, mousey - item - set position to background.x, background.y + 32
You could use a loop to automate it. The only tricky part would be picking the right object, but I am sure there is a way to do that, the just set the position to "background.y + 32 * loopindex" and so on.
For the process of laying out your menu it doesn't make a difference. Just use a method like Steven's example and note the relative values somewhere. For the game you then hardcode these offets, instead of letting the player move things around.