How to use a 180° skydome-only HDRI?


I’m stuck with an HDRI… I got a free HDRI skydome which covers 360x180°, i.e. only the sky. Blender maps it to 360x360°. I already tried playing with location, size and scale parameters but without real success.
How would I map this HDRI to only cover the upper hemisphere?


Edit it in photoshop (or other 32bit image editor) to add a bottom half somehow? Even if its black?

:D… Ok… Why complicated if it works simply too… Thanks!