i assume you have an android device.
you could try a reader app that has in-built the ability to fetch books from a local network - such as mantano premium with it's file browser. it is possible that such an app will be able to see the WD cloud and let you browse the calibre library in a basic folder tree- better than nothing?
to test that scenario for free, try doing it in ES file explorer - if fact that could be all you need. tell your device what app to use for opening an epub book, set up a favourites link in es explorer for searching - and then see if "opening" triggers an auto-download
all you should need for ES file explorer is the local IP address of your WD cloud, then set it up with the LAN section. This is how I access shared folders on my windows PC
if all that fails then there's the WD cloud mobile app !
GIYF
http://www.wdc.com/en/products/produ...x?id=1140#Tab8