How easy would this be to build (Optics, Photography)

Hello, any photographers out here would probably have noticed the rise of mirror-less cameras offering DSLR level photo quality. Problem is, the good ones are very expensive.
So I decided to try my hand at building one, after seeing a video on youtubeof a person who had made one out of the old nokia N8 (with it’s pretty good 12mp sensor). I have managed to get the case off and the lens mounted in the front of the sensor and everything seems to be working swimmingly.
However, the tiny N8 sensor converts all of my lenses into big telephotos (5x crop factor!). Some of you may have seen the metabonesspeed booster, which basically concentrates light which would otherwise be wasted from a FF lens onto a mirrorless body, decreasing the focal length and effectively making it a faster lens, working basically as a inverse teleconverter.

Now seeing that neat little device, I’m wondering how easy it would be to make a similar one for my N8? I know you can get individual lens elements pretty easily and I’ve had a bit of experience with custom (crappy) diy lenses. Would it be as simple as a cheeky achromat of the right focal length (and also, which one?)

The sensor in the N8 is very small compared to a DSLR or even the mirrorless cameras. It’s image quality will never approach the other cameras.

I know, but the pixel photosite size is comparable to other mirrorless cameras and that affects image quality a lot more than sensor size. Besides, this just for a bit of fun