space bar to move rectangular selection while dragging (like photoshop)

Hi, being a photoshop user I'm used to be able to move my selection coordinates while selecting by pressing the space bar while dragging a marquee square. That's very useful because sometimes you start a selection but then you realize that it needs to be a little bit more to the left (for instance) and you don't want to re-select, you just need to shift your all selection to the left.

Now in blender, pressing b in 3d view you engage a similar selection tool, however pressing space bar (once selection mode is engaged) does nothing. I suggest pressing space bar (while dragging) does move the whole selection, and releasing space bar then returns to the normal mode (where mouse movement defines the corner of the selection rectangle).

Hope this is not too confusing.