[wulf]

Focus on something else. Do you know how to do a "bokeh" shot? You would use that kind of set up - focusing on a nearer subject and allowing the narrow depth of field to cause the background lights to blur - but the mask will give them shape.

Coloured paper might work but black is probably better - stopping light going through and also stopping it reflecting back from inside the camera. You could always go over your mask with a black marker pen.

Wulf