How to control when which passes are rendered?

as I understand it, Unity draws all passes of a shader after each other. How can I get more control of what gets rendered when?

I would like to achieve the following:

1. render each of my objects into a renderTexture using pass1 of my shader

2. do something with the renderTexture (i.e. apply some fullscreen effects using another shader)

3. render each of my objects to the framebuffer using pass2 of my shader

How can I achieve this?