I shoot in UHD but finish and export in a 2.39:1 anamorphic-like format, so it's helpful to have a frame guide on screen to give me an idea of the framing during the shoot. And a6300 does have one. 

However, the 2.35 frame guide built into the camera only works when using the XGA viewfinder. When using the LCD screen on the back of the camera with a 16:9 native display aspect ratio, the frame guide will be streched terribly in the horizontal axis, yielding a completely unreliable and thus unusable frame guide.

I know an external monitor can solve the problem, but that brings about more issues like (even) more batteries, and larger size. 

Can this issue be addressed via a firmware update or is there any other workaround at all?

Thanks.