gistfile1.js

var _that = this;
jQuery.extend({
  someFunction: function(onSomeEvent) {
    var variable = 'some text';
    onSomeEvent.apply(_that); // how to pass current scope variables/functions to this function?
    return null;

    function _someMethod(arg) {
      console.log(arg);
    }
  }
});

jQuery.someFunction(function(){
  console.log(this.variable); // or console.log(variable);
  console.log(this._someMethod(1)); // or jQuery.someFunction._someMethod(2);
});