I best job I saw so far is to build a wood frame, wood frame is fixed on the wall with four big screws ( you have to find the sud in the wall). and a door built in. One side has board. I helped my fried took it down and seal the hole with drywall compound and sand the wall, You could ask minto for little paint and cover it up.
Minto does not say you couldn't nail the wall, they just say how the room when they give you, how the room when you leave.
It was done by another friend who used to be a carpenter with right tools. Cost about 250. But if you don't have the right tool and skill , you wouldn't be able to get the same result.