In MEP14+ you can use the blur effect. If it is to be constant for the object use the realtime visual FX editor window [Shift+Y], click on 'Blur' button and drag your mouse across the sensor ball to vary the strength. If you want to vary the strength with time you use keyframe animation available from a right click menu.
In VPX2.5 (and presumably MEP16 or 17) the blur is under the effects tab 'Video effects' >> 'Sharpness' where values less then 50% cause softening rather than sharpening.
There is a limit to how much you can blur, but if you need more you could apply the maximum, export the object as a new video clip and then import it and repeat the process.