I may have not understood what you meant by a panel.
When you copy an element from the hierarchy tree, you can only paste it at a similar parent level.
So if you have a map window with a deck with cards, the map is branch level 1, the deck is branch lvl 2 and the cards are branch lvl 3.
Card can be copied individually to any deck.They can alos be copied individually to a Game Piece Palatte, in a panel for example.
Deck can only be copied to a map. You need to right click on the map (same or another) to paste.
In fact, as there is no option to create a deck in a Game Piece Palette, at root level or at Panel level, you can't obviously paste de the deck there.
As suggested by jrwatts, you may need some day to edit the buildfile to do some bulk modifications.
It's not that hard ... you just need to leave the comfort of the graphical interface, and use a text editor.
As we deal with XML syntax, you would not be able to destroy that much

.
But, now that I think about it .... why do you want to copy all the cards from a deck to a panel ? Deck cards are individual disctinct elements. If you place them in a Game Piece Palette panel, you would allow users to create unlimited copies of the same card !
There may be a misunderstanding of the use case here. Can you detail your needs ?