Alright i have found that it is really easy to max out you sneek skill this way...

1: you need to go to a walled area or a place were you can walk into something constintly and never move.

2: walk up to the wall.

3: get into sneek mode

4: now i used a rubberband but you can use anything that holds down the stick for a period of time.

5: now you can leave the room and do what ever you please. i went to a friends house for a while and when i came back about 3 hours later my sneak skill was maxxed out.