Ok, first, does your JCS have the trigger zone event? If not, replace the 246 event in JCS.ini (located in the same folder as JCS) with the following line:
246=Trigger Zone |+|Trigger |Trigger|Zone|TriggerID:5|onoff:1|switch:1
After that, place a trigger zone event somewhere in the level. Turn "onoff" to 1, TriggerID to whatever is the TriggerID for the Trigger Scenery you want to trigger, and leave Switch on 0.

For more information, see EvilMike's article. http://www.jazz2online.com/articles/view.php?id=32