also how good does your solution work if the itunes library is huge so that the library file is over 100 MB ? Then your solution will not work well.

the libray I use has 70GB+ and the only drawback is that when I initially click on the shared library icon (on my local computer that has the VPN client), it has to fetch the library information which takes about 30-60 seconds. But since I do that only once a day, I can well live with it.

my libray file has 26 MB.

Why do you assume the built-in sharing will be less efficient than copying the whole library file around?
I don't really know how the daap protocol works, but what I observe is that the transferred data with the initial connect is definitely less than the filesize of the library file.