Hello there,
We are actually offering this as a new 4 night extension on our 2014 dates, so you are right that it is something worth doing.
For the 2013 dates, although an excursion is not offered, it may be possible to arrange this direct once in resort. Depending on the island you want to visit, ferry crossings from Cefalu to Lipari take approx. 1hr 45mins. Different islands would take longer... Having a look on the internet, prices of excursions to and from Lipari start from €60.
I hope this helps, Sally-Anne