I have forked the Polymer-Project and made some changes to it work on Opera12.
I'm using the in a huge portal project that uses RequireJS, so I'm not using the ShadowDOM features from Platform because it need to be loaded before the DOM Ready and the require uses the DOM to add scripts.
I haven't finished work yet, still have some bugs like when using console to create elements, the TemplateBinding doesn't work as expected.
There is also some shim I'm using that isn't on github yet, but if someone has interest in the Opera support, I can share it.