You should be able to mount the NAS via URL, IP or UNC to be a Windows share or mapped drive. This should give you the OneNote access you require.
http://www.wdc.com/wdproducts/library/UM/ENG/4779-705103.pdf
WD My Cloud manual link.
Many NAS devices also come with the ability to connect to the device remotely. If your device doesn't then you could set up a home VPN and access the files as if you were at home.