Load up either Assault on Asgard or Stitch's Tropical Rescue (duh) from the extra little hexagon disc you got with your set.
Load up the game. **Now I didn't check if you can do this in the tutorial, but in the first level** you will select a "trap" (Turret, wall, mine, etc) in your inventory. You will then go into weapon placement.
Just place the item. Then press Y (sell). And then press A (place) and repeat 50 times.
However if you are going for 90 feats, you may as well actually play thru the mini-game and get some of the other feats (like place 6 different types of traps in a session) so you'll otherwise get this achievement in due time.