[GLSL] Access to Overdraw

Pretty basic question:
When using Blending and Sorted Draw with Blending in a Rendersetup, is there any chance to gain access to the pixels which got rendered before the current material is rendered, or is this happening in the render itself?

Example: Could I get access to the data that is presented in the renderselect in the shader that is applied to the “top” GeoComp?

You would need to use multiple Render Pass TOPs for this. The depth peel layers in the order independent transparency workflow are also likely want you want, if you can use that.