DS24B33/DS2431 eeprom

first to connect to get to the prototype via a - throw-away - instance?

Who said it was throw-away?

var eeprom = require("DS2xxx").connect(...);
eeprom.__proto__.constructor.prototype.read123 = function() {
  return ....;
}
eeprom.read123();

I think that's fine, and it has the nice side-effect that we don't have to re-write any of the existing modules.