Copy-pasted this part from the mini wish list:
"an easier to use copy paste: It's a pretty simple concept, and could even be a little check box in the advanced build, or whatever. The way it works is you bring up the copy, click on one block with left click, the other with right click, and the cube created by the vectors is now the copied area. Paste wouldn't have to be changed. No more having to pick a precise box using the sliders."