Lockpicks:
1. Sell them or
2. Open your inventory, drag the lockpicks out of it and before you let go of the mouse, press CTRL. A pop up window appears, the one you know from trading
Kiya
Raze explains it like this
Drop the lockpicks on the ground, then drag them into your inventory and hold the control key down before dropping. This will bring up the split stack pane, which will let you specify how much lockpicks to drop into your inventory.
