Giving the lens and one map piece to Wally is an interesting one. The thing here is that, while Guybrush is giving him the lens, you can open the inventory, which is unusual. However, there are a few frames where clicking on the map piece, won't select it.

1. Before entering Wally's, make sure the lens is on the first row of the inventory and it's also the current item.
2. Hold Tab while entering Wally's so Guybrush starts walking immediately, and keep holding Tab while you lower the cursor so it's approximately on Wally's hands. That way it'll be on Wally's hitbox, but outside the inventory area once you open the inventory.
3. Open the inventory, press Enter to select the lens, close the inventory, and click on Wally.
4. Open the inventory, click on the map piece (don't be too fast here), close the inventory, and click on Wally.