AFAIK you can use the ENB Injector version with vorpX. You can download it from the ENB mod website. This wasn’t tested here, but supposedly it works.
To enhance the image quality you have various options in vorpX: One is to set the game resolution higher than the Rift’s default 1280×800, which forces the Rift to downsample the output, creating a generally better looking image. Whether, and if, how good this works depends on your graphics driver and settings though.
vorpX also has various image quality related options on the display tab of the in-game menu. Try enabling ‘Fix Chromatic Aberration’ or ‘Shader Antialising’. Using both together is usually overkill and might cost you a few FPS, so try the one you like better.
Hope that helps.