This is based on a idea stolen from Warhammer Quest: Silver Tower box set. Its got some very D&D'able ideas.
When someone attempts to pick a trapped lock - rather than resorting to boring skills checks - take a playing card, (or if your a fancy pants like I am - draw a padlock on a bit of paper the same size.) and make a tower from 2d6 on it.
- The player must pick up the card from the table with one hand without spilling the dice or touching them in order to spring the lock.
- If they touch the dice, their lockpick is broken - the GM resets the challenge.
- If they spill the dice, any trap on the lock is set off.
- EDIT: If they have no thieves tools plus there's no trap .. go through the same process and if they spill the dice the tumblers in the lock are jammed/frozen -- now the lock must be forced open with a STR check or some other creative method.
Its very doable, but requires some patience .. and a bit of practice. Its a focus on very literal player skill that old schooler's bang on about, AND explaining the rules to the players takes about 30 seconds, so you don't have to worry about muddying the waters with games-within-games. #winning
Also! Make things easier/harder by stacking less/more dice. If players have fancy thieves tools - less dice, maybe if the lock is magical and enchanted you swap the playing card for a bigger thing? Have a play, you get the idea.
EDIT: In a conversation with the super talented +Karl Stjernberg its become clear that its the tension of failure that makes this mini game interesting. So, Im going to rule that thieves with appropriate tools can open any lock, given enough time. However i'll use this method if there's some time-sensitive thing going on OR if the lock is trapped. I'll probably still use the method above if they have no thieves tools too.