Personally, I reckon the solution would be to try and mount the fan higher up the heatsink. How about bending the wire pins or something like that? [Note: I haven't tried this, so its meant as a suggestion at your own risk!]
The other solution would be do to away with attaching a fan altogether and get a P180 case instead. The 2x120mm case fans suck hot air away from the Nina perfectly. I get 33c idle using the bare heatsink and the two P180 Antec Tricool fans at their lowest settings.