You will need to make a plugin based on IHeadMountedDisplayModule or IStereoRendering (IHeadMountedDisplayModule is probably better because it will get loaded automatically by the engine). In there you need to implement GetStereoProjectionMatrix() and CalculateStereoViewOffset() to set the matrices. Search the engine source for FFakeStereoRenderingDevice or the Oculus plugin, I used those two as an example when I implemented it.
Also in a cave you will have an off-axis frustum, temporalAA does not play nice with it right now but you can disable it or apply this patch: https://github.com/EpicGames/UnrealEngine/pull/912