Open your inventory, drag the money 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 small pile of gold on the ground, then drag a pile with more than 2002 gold 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 gold to drop into your inventory.
