With your solution you would have to add it for every single account. Isn't it possible to do it for all enabled accounts with one command?
/usr/bin/dbus-send --type=method_call --print-reply --dest=org.freedesktop.Telepathy.AccountManager /org/freedesktop/Telepathy/AccountManager org.freedesktop.DBus.Properties.Get string:org.freedesktop.Telepathy.AccountManager string:ValidAccounts