Zdepth (Fog) with motion blurred renders?

I'm working on a full CG shot with all passes rendered in VRay and was hoping to add my depth cue / fog in comp. However, I'm running into issues with the Z coverage on heavily motion blurred frames (using 3d motion blur in my renders) which is not totally surprising. Does anyone have any advice on way to reduce the artifacts caused by this, such as filtering options in VRay, etc. Thanks!

I'm going to try some tests going "old school" using filtered and clamped zdepth with a defined range. This might do the trick.