[Adam Skelding]

Here's a real cheapskate way of doing it.
You could always glue 2 deans connectors side by side. Do the same with the female, using the male as a Jig.
Cut the redudant 4th terminal off using a dremel slitting disc or such. That way you save your 4th termnial to add to another full deans block.

Making sure you can only plug it in one way is simple enough. ||-