buried shovel
n. A tool that is required to perform a certain task, but that is only available after you perform that task.

Example Citation:
"A number of readers wrote in to complain about the 'buried shovel' trick: modem vendors whose installation help is available only by modem, or hard drive vendors who include installation manuals as files on the drive."
—Fred Langa, "What's Up, Docs?", Windows Magazine