personally i'm a firm beleiver that 'variety is the spice of life'. pens or other sharp tools such as forks or knitting needles as someone mentioned, can be helpful in unlocking your lee's ticklishness. once you've opened that door even a crack ( lol) everything will tickle him/her, even things that might not normally tickle. it's all in the mind! i think strategy is in order, always, also threatening your lee with devastating tools such as pens might work miracles. then when you only use fingers, he/she might be initially releived, only to find that he/she is now helpless against just about any type of tickling! and if you THEN switch to 'mean' tools...boy oh boy! just the sight of them might trigger a flood of giggles, pleas, etc..before anything's even happened!
now THAT's power. 😀