My attempt at doing this failed on HardFP/SoftFP incompatibility.

Fremantle is SoftFP build, Harmattan is HardFP build.
So N950 3D drivers built for Harmattan's HardFP do not work in Fremantle SoftFP env. And Hildon Desktop requires accelerated graphics to be usable.

There are possible avenues to work around this, but these are so time consuming, that I gave up.