To make it smaller, you could use try using right angle headers, or even some kind of right angle extension to make the icsp header less high. You also might try finding a lower height potentiometer, maybe even a surface mount one. I also think it would be interesting if you could make a case for it, to make it a little less obvious. Ie, make it look like a normal flash drive or something. For extra confusion or distress, tack on the label of a manufacturer the victim has other peripherals from.