Calling GL commands from the rendering thread

I am currently working on a research project for an ambilight-like system for oculus rift. Therefore I need to render to a Texture (which works fine) and download the Texture from the GPU to the CPU. Now I know that there is the ReadSurfaceCommand but it is so slow that it drives my GTX980 ti into the ground (roughly 25ms for a 2000x50 sized Texture). So my next idea was to directly call glGetTexImage to retrieve the texture. Any ideas how i can achieve this (or something similar)?