Using different normal map channels?

Still new to UE4, was wondering if there is a quick and dirty way I could hack in normal maps that are packed differently?
I’m doing an experiment with an open source game that packs the red channel of most normals into the alpha, and the green into the blue.

Use Append node to create vector2 from blue and alpha channel. Then multiply this vector by 2 and subtract 1. Then use DeriveNormalZ node to get Vector3.