Could try file system in userspace and mount a cifs (samba) drive
-
First install the cifs package
opkg install cifs -
Edit your /etc/fstab file for a permanent mount
//<IP address of NAS box 192.168.x.y>/<shared folder> /<mount point> cifs user=<user on NAS>,pass=<passwd on NAS> 0 0
Just lookup mounting samba shares on Google or something