I have been manually putting recyclers (while my server is low pop) in each of the tunnel stations -- where the tunnel stations have fork lifts, back in the dark corner. I also add them inside the barns, on the second floor, to give a use for those specific locations. Otherwise, there's no reason to go up there. 

"spawn recycler" (I think it was) in console. It's not permanent, though. I don't recall if they're lost after a restart or through a wipe.