Is it feasible to make a sealable hole in the freezer door seal?
Put the cord/hole in the top of the door, and it really won't matter:

The cold air is heavier than the air around it.  So your freezer full of cold air is like a bucket of water:  the cold air is trying to flow out only where gravity will let it.  Other than the stirring of air causing the mingling of warm and cold air, a freezer doesn't need a top at all.  Ever wondered how the open-top freezers at the grocery store stay frozen?  They're a big bucket, and the cold air is trapped by gravity.

So take advantage of that:  Put your cord inlet at the top of your freezer, and don't worry about sealing it.  The mixture/transfer of air at the cord inlet point will be negligible.