A long, long time ago I created a script for Arma2 to spawn AI units by placing them in the editor, then the script delete and store them for future use complete with waypoints and all. But Arma 3 apparently removed vehicle inits, so this is a revised version. Not sure if anyone has already had the bright idea to fix it, I just got Arma 3 myself and is completely out of the loop in the scripting news. So I recap my original words: If a simple editor based triggered spawn script already have been done - well then this is a repost, lol!
Example mission on Stratis (zip)
The .sqf itself contain all the info needed on how to use it. For the mission, just visit the sandbags. Or poke the dead person. Some trigger hints still left in (mission only, not in the script). NOTE: No idea if it works in MP. Never tested in the original, not tested now either. Works in the example mission at least :p
Original script on Armaholic - Do note that this A3 test version is scaled down a bit and just contain the primary spawn sqf, havent gone into details with the changes that ArmAIIholic did.
Edit: uploaded as a regular zip file instead of 7z