Transparency for all 3d models in a game object

Hi,

We are looking for a way to create transparency (going from 0% to 100%) for all 3d models within a certain gameobject. The tricky thing is that almost all of the models are using different shaders, and many of them does not have an alpha channel. If they did have an alpha channel it would have been a lot simpler

We have a few ideas ourselves on how to do this (not so sure if they are good ideas though) so we wanted to hear if anyone else has an idea for this?

Hope it's clear what we want to achieve.