'This' properties inside Polymer objects

I am trying to make a plugin for Tern to be able to support autocompletion inside Polymer elements.
At the moment I am able to access the properties that have been directly declared, but not the ones inside the defs.json I have created.

Assuming I have something like this:

‘!name’: ‘polymer’,
‘Polymer’: {
’!type’: ‘fn(config: +Polymer.Base) -> +Polymer.Base’,
‘Base’: {
’!type’: ‘+Polymer.Base’,
‘prototype’: {
‘set’: {
’!type’: ‘fn(path: string, value: ?)’,
’!doc’: ‘Convenience method for setting a value to a path and notifying any elements bound to the same path.’

I would like to be able use this.set() inside a Polymer.Base element. Do you have any idea how can I accomplish this? I think that the problem is the prototype of the ‘this’, because it is not ‘Polymer.Base’, but I am not sure how can I do it.