Saving Gmail attachments to an existing card in Trello

[PE Gmail]

I've installed the add-on Trello for Gmail. Everything seems to be working, but the only function I see is it lets you take an entire email, and create a card from it. Not very useful for me. 

I'd like to be able to save information or, specifically, Gmail attachments like PDFs, to a specific existing card in Trello.

Is this possible?