Rendering Transparent Objects into RenderTarget by using shader

What I want to accomplish is to render only any transparent objects in the scene without any postprocessing effect applied.

I’ve created a Custom Camera Actor with SceneCaptureComponent2D and RenderTargetTexture, and maybe ready to go.

Then, with SceneCaptureComponent2D, I’ve made the SceneViewExtension, such that I can attach my custom shader to it. One of the examples I used is Global shaders in Unreal without engine modification - Caius' Blog, but how would I be able to tell in the shader whether the object has transparent or translucent materials?