Create a subnet. In your subnet just create 2 nulls IN and OUT (just gonna be easier to deal with). In the Basic tab of Operator Type Properties make your subnet an editable node.
Then you can have a button to call a script in the python module to create and insert whatever node you want.
You just need createInputNode() and setInput().
Or in your case, using a connected node you could fire the python module script using On Input Change. get the operator type, then create it, input it.
should work.