The easy way of converting is to just put two mediums on a bottom board. Put the nuc frames all the way to one side and fill the rest of the two mediums up and down with medium frames. As the bees expand into the center of the two mediums and the outside deep frame has had all the brood emerge, remove it and slide the next deep frame to the outside position and fill from the far side up and down with medium frames. The deep frames will probably be full of stores. To save this just lay the frame on the top bars and let the bees rob it out. After it is robbed out, it can easily be cut down with a table saw or the wax salvaged for candles. It is just not a huge obstacle.
I agree with Vance. I've seen it done this way with no problems.