How to create virtual properties in Kohana 3 ORM

Question

I have a timestamp field in a model where the time is stored in UTC. I would like like to create a 'virtual' property that allows me to access the model using local time based on the timezone property also stored in the model. That is when I get the local_started_at property it reads the started_at property and adjusts the value based on the timezone property.

What is the cleanest way to go about this?

function doit()
{
    bob = ORM::factory('user')->where('name', '=', 'bob')->find();
    bob->timezone = 'Vancouver/America';
    bob->local_started_at = '2010-08-11 08:00:00';
    bob->save();

    echo bob->started_at;
}

Output would be the UTC time for 8am Vancouver time (3 PM UTC).

2010-08-11 15:00:00

The main purpose will be to take input from a form that allows users to work in local times.

My attempt at overloading __get and __set does not appear to be working.