Steve's keypad routines won't let you reverse the orders like that.
But you can re-map the keys to whatever you want.

By reversing both the columns and rows, I think it would come out like this ...
Code:
@ READKEYPAD _myvar

; original keys   1  2  3  4  5  6  7 8 9 10 11 12 13 14 15 16 
LOOKUP  myvar,[0,16,15,14,13,12,11,10,9,8, 7, 6, 5, 4, 3, 2, 1],myvar
Which should also work like this ...
Code:
myvar = 17 - myvar
If they don't line up right, you can change the LOOKUP to a pattern that matches.

hth,