Validation errors and file uploads

I've got a form that contains a number of textfields, as well as a file upload element.

I've noticed that this field doesn't retain it's data after validation errors. While I know html/http doesn't allow form fields to be pre- populated per se, it can be faked by stuffing it into the session. Yuck.

Is there any accepted pattern/best practice for faking it that doesn't require the file to be tacked to the session?

I should say that I'm using rails 1.2.6, and this is self-rolled file code in the controller and model.