Thats easy!
If you were doing it via ↑↓←→, then it would look something like this.
SPSET 0,0,0
WHILE 1
B=BUTTON()
IF B AND #UP THEN DEC SY,16
(Repeat above changing variables respectively)
WEND
By decreasing SY, you make the sprite go the same length as 1 whole BG Tile.