I just came across this as I was having a similar issue.

the only problem is that I have to call this in a view with @model in order for it to work, otherwise attributes will always be empty

The simple answer is that you can't because without the @model directive defining the type, the view assumes that the model is dynamic and so the HtmlHelper parameter of the extension method will actually be IHtmlHelper<dynamic>. That is my understanding.

If you have since found an way round this, please let me know.