Thanks guys, this will do for now.
By the way: What you're doing with that clip() should be possible with the depth buffer directly, no need to bind it as SRV. Draw your full screen quad with a fixed z at that threshold value and use a depth comparison of greater or greater-equal. Or set z to 1 and the comparison to equal (if your depth was cleared to 1 initially).
True, but when I started I was not sure if I wanted to mask pixels out or only include them with a smaller alpha, so I thought this would be more flexible, though, perhaps not as efficient as your approach.