Could get someone to make a custom shroud out of black perspex or black sprayed metal?
If the card has "space" at the edge of the PCB, simply use some plastic clips on those bits? If not, create a bit of mesh in each corner that goes to nearly touching it and use arctic ceramic or glue/blue tack etc? depends how nice you can make it look I suppose, but you could always not have mesh on the corner bits and have it solid?