Yes, I would probably make each "sticky" area a hotspot, and have the objects (posters) placed on top of it, and the objects will turn on once you put posters on the sticky spots.
For using inventory on a hotspot, go to the hotspot interaction screen and look for "Use inventory on hotspot". Double-click it to make the action editor window appear. From the drop-down box, select "Conditional - if inventory item was used". Then click the "Change" button and enter the inventory item number for poster #1 (the number next to it on the Inventory items tab in the editor). Then put in the code for the character to walk up to the wall (MoveCharacterBlocking, or you could just assign a walk-to point for the hotspot and then use MoveCharacterToHotspot instead), then another code to put the poster on the wall (ObjectOn), and finally one to lose the inventory item (LoseInventory). Do that for each poster on each sticky spot, and you're set.
~Wolfgang
For using inventory on a hotspot, go to the hotspot interaction screen and look for "Use inventory on hotspot". Double-click it to make the action editor window appear. From the drop-down box, select "Conditional - if inventory item was used". Then click the "Change" button and enter the inventory item number for poster #1 (the number next to it on the Inventory items tab in the editor). Then put in the code for the character to walk up to the wall (MoveCharacterBlocking, or you could just assign a walk-to point for the hotspot and then use MoveCharacterToHotspot instead), then another code to put the poster on the wall (ObjectOn), and finally one to lose the inventory item (LoseInventory). Do that for each poster on each sticky spot, and you're set.

~Wolfgang