Item in hand procedures

I would like to recreate the flint sharpening mechanism from Sevtech: Ages where a player can left click on a stone block using a piece of flint and have a chance to receive a sharpened flint piece in return.  

The logic I'm wanting to use is essentially as follows:

when player left clicks a stone block while a flint piece is in hand

     100% chance to shrink flint piece item stack by 1

     10% chance to spawn sharpened flint piece where player clicked

I cant seem to figure out how that would look in the procedures menu and would love some help!