The reasoning is the same and stated in S.A. O.C 253:5- it isn't the normal way of cooking.
Solid foods that have been cooked or baked are no longer subject to its respective melacha of bishul (ain bishul achar bishul). Placing the item on the stove from, say, the fridge is at best rabinically forbidden because it appears to others like you are cooking (michzei kemevashel- I don't recall whether we are worried about how you look or about their assumption of the halacha). The sages allowed you to place the food in an area not normally used for cooking as this circumvents the issue.
So putting the item on an urn or on top of a crockpot (but not in the casing or on the surface of a slow-cooker) would be fine.
This is true even by "cooked" items (through water or steam) since the heat source is not performing a true roasting. However, you should not wrap the food in addition to its initial covering as this would violate hatmana.