Is there a way to change/set the filename on download?

Example: Jon Smith uploaded his headshot, and the filename is `4321431-small.jpg`. On download, I'd like to rename the file to `jon_smith__headshot.jpg`.

View:
`<%= url_for user.headshot_file %>` 

This `url_for` downloads the file from Amazon S3, but with the original filename. 

What are my options here?