Attachment URL vs. file

We are using a custom object for attachments.  This allows us to track a variety of information about the attachment - author, document business type, review history, etc.  The custom object approach also allows us to build reports that include information about the attachment (document).  I'd like to find a way to NOT store the document in the CRMOD DB.  Instead, I'd like to store a URL that references the physical document.  When an attachment is in a related list, a URL is an option.  I'm not seeing this option when using the custom object approach.  Is there a way