I suggest, while press-holding a pattern button, select and press the pattern button to copy to. quick, easy without using other knobs or getting in the way of anything else!
you wouldn't be able to copy pattern A-1 to C-8 (unless you'd want to implement holding down four buttons A, 1, C, & 8 ).
I'm guessing the source would be blinking waiting for a Pattern press or the usual sequence Bank, then Pattern.
Example:
1) press A (lights up A)
2) press'n'hold 1 (1 starts blinking with display msg "Copy Pattern to..." and all the other buttons light up)
3) press C (message still shows the same msg but bank buttons now are off, only C is on and pattern buttons are all light up still waiting)
4) press 8 (msg now shows "A1 copied to C8" and now only C and 8 are light up).
Maybe a variation of this would be to press'n'hold the target to force a move (or swap, maybe?) instead of a copy.
EDIT: Of course, if the copy/swap happens on the same bank, the sequence would be:
1) press A (lights up A)
2) press'n'hold 1 (1 starts blinking with display msg "Copy Pattern to..." and all the other buttons light up)
3) press 8 (msg now shows "A1 copied to A8" and now only A and 8 are light up).