Partial Backup / Restore Sql Server Simple Recovery
In short, no, you can't backup the individual files that you want to restore. According to BOL, the only way to backup files on a database that uses simple recovery model is if they are all backed up up together: http://msdn.microsoft.com/en-us/library/ms179401.aspx .
Have you considered differential backups of the files? Doing this would give you smaller file size for backups (still requires a full at some point), but would also increase the number of steps required to restore the database. Differentials partial backups are described here: http://msdn.microsoft.com/en-us/library/ms190218.aspx.