This is actually been done many times in history. Most technical information handed down through the ages, such as alchemy, has been transmitted by various forms of allegory which make absolutely no sense to anyone who does not know the symbology used.
However, the best way to hide instructions is to hide it from everyone, even the one's carrying out the instructions, is to encode the instructions into some kind of ritual. For example, many technologies handed down from generation to generation come with a ritual, which makes sense because traditional technologies were created by trial and error and the artisans who manufacture the technology, have no idea how it actually works.
I have read that the complex rituals guide the creation of the steel for Japanese swords. The rituals contain elaborate chants, and there are different chants for different seasons, different temperatures and even different types of ore and charcoal. The chants are religious in nature, various prayers for this or that. But the content of the chants is utterly irrelevant, its the time the chants take matter.
Just a couple of days ago, I saw a video on medieval armor making in which the armorers used powerful chemicals, mercuric chloride IIRC and various acids. Timing is critical for the process and is the differences between status decoration and burning a whole through very expensive steel. It is believed that the armorers used a certain count of Hail Mary's to time the reaction times. (Modern researchers are not sure because in a time with no patents or other intellectual property protection, artisans kept their processes as secret as possible.)
Work songs have long been used to coordinate teams. "What do you do with a Drunken Sailor" regulates the rhythm of raising a sail, "Way, hey and up he rises," refrain repeated three times gets the sail pulled up. The verse "shave his throat with a rusty razor" lets the landsmen to move to another line.
A dance could be used to encode the operation of a device, especially if it used a visual interface like an Xbox Kinect.
In addition to timing, songs and poems are innate mnemonic devices. Individuals can remember them for decades and hand them down to subsequent generations little changed.
Used to be something of a trope in science fiction in which following some fall in civilization, the management of remaining technology becomes sacred and is managed by priest or monks who carry out operations as religious ritual. Kind of the same thing.
A religion group could watch for some sign, like the appearance of a an asteroid in a constellation, which would trigger a religious ritual which would activate a weapon to blow up the asteroid (I think that was a Star Trek episode.)
Alternatively, you could hide the information inside a taboo or the practices of low social castes. Kinda the cultural equivalent of hiding physical objects in latrines or septic tanks.
If you want a purely mechanical method, a hologram would work. When you break a holographic plate each fragment retains the the entire original hologram but at a progressively lower resolution and more shards of the hologram are created. You could scatter them around until some trigger event causes people to bring their shards together until enough of them were mated to produce a high enough resolution to reveal the instructions. (Gibson's "Fragments Of A Holographic Rose" is one of my favorite stories.) You can do something close by stacking polarized colored lenses, each with small defects which, when lined up in the proper sequence in the right light, projects a pattern that can contain arbitrary information.
All of these behaviors would seem nonsensical to both outsiders and those carrying of the operations. It would be program running on wetware that no one even knew existed.
(Actually, figuring out just how cultures encode all kinds of information in what superstitions and rituals has become something of a hobby of mine. I'm not sure we've stopped doing it even though we can write down detailed instructions theses days.)