I'm confused what spoilers you mean. You should only lay out the items you have unlocked (Prosperity 1, Prosperity 2, etc.). If you unlock a pattern you can right-click and "Search" the Reward Items deck, and type in the name of the card you've unlocked, so you don't have to look at all the other cards in there.

I've found that when I search the treasure deck, I can usually pick out which card it is just from the minimized picture before mousing over anything. So some of the general pictures of items get spoiled, but not what the items do. They also come in numerical order so you can sneak a peek at the number of one card and use that to orient yourself to where the others should be.

It does come down to a matter of willpower though. I can also ignore dirty socks in the middle of the floor for a week, so it's not problem for me.

I mean, you handle it the same way as you would if you played the physical version.. You look through the deck and pick the correct card. This mod is even less spoilery since you can just use the search field (Rightclick the pile -> Search) to directly find the correct card without manually going through all of them.