[Lizard]

Sorry, that feature isn't there yet. We hope to implement it soonish, but I cannot make any guarantees.

In the meantime, you could add a custom data column listing the path to a file, and then write an AppleScript (which can be added to your toolbar) which looks at the custom data column and opens the file for you. A little clumsy, but will work if you need file attachments *now*.