Is it really worth your time over-doing a heatsink for a $10 diode? It sounds like you all want him to put $50 of work into it. Yes, you could obtain a 3 pound block of copper and drill a hole in that and cool it with peltiers... but why? It's a $10 diode that will operate sufficiently with layered aluminum.
To take a $10 diode and overdrive it beyond specs so that it ends up being more than just a $10 diode.
If he's only going to power it within specs, then I guess he could just wrap the thing in tin foil and call it a day.