What you want you need to find out is what files the wakeonlan package provides which you can do with
$ dpkg -L wakeonlan
In this case the only interesting file is /usr/bin/wakeonlan which is a perl script
$ file /usr/bin/wakeonlan
/usr/bin/wakeonlan: a /usr/bin/perl -w script text executable
So find out if perl is installed on your NAS.
If it is then you can try copying the /usr/bin/wakeonlan file over to your NAS and see if it works. It might, or it might not depending on whether various other perl related bits that the script uses are also already on the NAS. If you've got perl on the NAS, but not other require bits, you can try working out which perl bits need to be copied over. The wakeonlan package depends on two other packages use
$ apt-cache search wakeonlan
to see them. The 'dpkg -L' command mentioned above will show you which files those packages provide.