Peeling the center fins of the heatsink (takes a few hours of patience with needle nose pliers/medical forceps) and zip-tieing a Arctic P12 Pro (or any other 120mm high static pressure fan) to it works pretty well. Note that you should probably take the heatsink off while doing this to prevent metal shards from shorting out your board (removing the heatsink might necessitate redoing the thermal pads/putty).

Most just 3D print (or buy) a manifold for a standard PC 12v fan.

I assume duct-tape and cardboard would also work if things are dire. =3