How to send a card to the bottom of a Deck
A Deck is just a special form of a Stack, so the stack manipulation commands (arrow keys) can be used to move cards around in a Deck that is not being auto-shuffled.
Of course you can't select on a card in a Deck in order to press the arrow keys, but you can send Key Commands to them using Global Key Commands, or Trigger Actions.
Say your Return To Deck trait is Ctrl-R. Add a Trigger Action 'Return to Bottom of Deck' that issues two Key Commands:
1. Ctrl-R to return the card to the Deck. 2. Down-Arrow to send the card to the bottom of the Deck.
Now you have a right-click command 'Return to Bottom of Deck' that will first return the card to the deck, then issue the down arrow command that will send the card to the bottom of the Deck.