Do treasures need to be drawn atomatically?

[Airblader]

Edit: title is supposed to read “atomically”, i.e., at once.

We were playing Munchkin Harry Potter and had the following situation: several players are Level 9, I am Level 8. There are two remaining cards in the treasure pile.

I beat a monster, and gain a level and three treasure cards. I take the two remaining treasure cards while a player starts shuffling the discards to replenish so I can draw my third. However, one of my two just drawn treasures allows me to pick any card from the treasure discards that I want. I ask to play this card immediately before replenishing (which would empty the discard pile), because I know the discards contain a GUAL card that specifically allows winning the game.

This led to a discussion whether I am allowed to draw treasures one by one and play them before moving on, or first need to draw all treasures (forcing the reshuffle). The rules don’t state anything here as far as I can tell. Is there a known ruling on this?