Its not cheating, he wants to make a proof of concept. There is no reason to waste time to redesign the whole interface.
I have done in the past similar work to show redesign of websites. I simply photoshoped every page and put them in powerpoint. Then when I did the presentation, I only had to 'simulate' the navigation by clicking on the image representing the buttons on the slide.
I used this trick a few times and no one ever noticed it. Actually, it can backfire if the client start to think that you can make a whole site in a night, he will find it suspicious that you ask for a 2 week pay...
This concept can also be applied to 3D: when you model something that will stay in the background, you can fake many of the details with texture. This is why scene planing/story board are so important.
Anyways, in case of doupts, I guess we can email the guy and ask him!