Sorry - not the actual metal sniffing. I meant that figuratively.
Essentially control Rooter - tell him to go into that "back of jet" thing (as I describe it) on the first screen in the scrap yard (to be clear - not where you get Mule, but the next screen - next to the Carbonite George Lucas).
Once you're "there" - get something - then actually use the metal sniffer to get something else.
That said, move Mule down to the next section before doing this (I found this helps preventing the Eternal Mouse Spin when you use Rooter to get something over there).