open your inventory, click and drag a teleporter stone, press shift key, bump the screen focus up a bit, drop the teleporter stone in the middle of the courtyard somewhere, release shift key
run in, get stopped by the guards, exit the conversation and immediately click inside the castle again (pausing the game as soon as the conversation ends can help with that).
BTW, the '
Lost Items' technique does not work well for items with random stats. This is described in the post.