You can initialize a collection of FileDataType and whenever you add an attachment to your DB, add it to this collection as well and then you can display the attachments using the DownloadList component on the approval form. The way I attach files from a workflow to a Helpdesk (6.5) ticket is to simply email the attachments so that it appends them to the ticket. The only downside to this is that files can't be larger than 10 MB as per our email size limit.
Since you already have the path and file name of the attachments can't you just write a query to get this from the database and encapsulate the result with HTML hyperlink tags? You should have some way to distinguish which attachments belong to which ticket.