well I have been reading on this site and I have to say...there are alot of helpful tips. Like the girl who said that she still lived with her parents. I'm in that same situation. But my mom knows I used to do it...although she doesn't mind now because she doesn't know when...I still live in fear she can hear me.
Often times when I am out with my gparents at lets say, a mall, I will try on clothes just so I can masturbate. I go into a dressing room and basically, for lack of better terms, 'hump' the edge of the chair. It gets me off within a minute...at the most two. Or if they chair is round turn it upside down. and 'hump' the leg.
These work really well.
Even though I know that they are a lil odd.