Some publishers want to add additional content to custom ebooks they are creating. This content may not require slicing, such as journal articles. It's easy to upload such content.
Login to your Slicebooks account
Click on "Uploads" link in the dashboard
Click on Upload Content button
The Upload wizard will take you through a couple of easy steps. This content will be uploaded to your Source Files dashboard. From there you can add it to new custom ebooks, slice it, publish it, edit the metadata and so on.