Object transparency separate from shader?

Hi I have multiple objects, all with different shaders and when I spawn them I would like them to fade in. I know the best way to do this is use the alpha to fade them in, which is fine. But my problem is that some shaders don't have transparency, some have multiple materials etc..

So I was wondering if it was possible to make some kind of game object transparency override? Like a script I could apply to all objects that would give me separate control of the objects transparency.

Thanks