Not sure if you can (easily) do that, but in the case of the fridge fan, I think the biggest benefit is that the air circulation keeps the ice and condensation off the fins, which then allows the fridge to cool better. The increased air movement is kind of a secondary benefit as far as cooling.
In the freezer (at least in ours) there is no drain, so even if you move the air, ice crystals will still form someplace in the freezer and it will need to be defrosted. In our little freezer, everything stays frozen, just get ice buildup that has to be defrosted after a couple weeks of continuous use.
2005 F-150 FX4
2013 Rockwood Roo 23 IKSS