You can do this by using the pixel_x and pixel_y vars to displace atoms' displayed position by pixels, and manually doing the whole movement and checking process (the pixel_* vars simply grant a graphical effect and no actual movement or collision checking).
However, the result of doing this fully tends to be sluggish in multiplayer, so you'd generally only want to do that in single-player games, or multiplayer games that are ran client-side, meaning every player starts his own server/BYOND world to play, and all those servers communicate between themselves to synchronize the game.