Polymer 1.0: How to pass an argument to a Polymer function from an attribute?

You could utilize HTML5 data attributes instead. Try like this:

<paper-button id="foo" on-tap="bar" data-args="foo,some other value,2">Click</paper-button>
...
<script>
(function() {
  Polymer({
    is: 'example',
    properties: {...},
    bar: function(e){
      var args = e.target.getAttribute('data-args').split(',');
      // now args = ['foo', 'some other value', '2']
    }
  });
})();
</script>