mod-return currently swaps the focused window with the master window. What I want is to move the focused window to the master and have the rest move over one place. So the end result is as if I had pressed mod-shift-k a couple of times.
Xmonad.StackSet.shiftMaster does exactly that.
Simply add a line looking like this to your keys configuration:
, ((modMask, xK_Return), windows W.shiftMaster)
Or, if you use
, ("M-<Return>", windows W.shiftMaster)