Overwrite functions(methods) on script side

[2beers]

Hi everyone. I'm playing with QScript module and I'm following this "tutorial":http://doc.qt.nokia.com/4.7-snapshot/scripting.html .
Everything is nice, but I couldn't find a way to ovewrite a function(method) on the script side.
Let me show you what I wanna do, so you can make an ideea:
On C++ side let's say I have a class that implements QRunnable

@ class HelloWorldTask : public QRunnable
{
void run()
{

 }

} @

Now I want to do something create many HelloWorldTask objects on script side, and overwrite the run method. something like this:

@var task=new HelloWorldTask();
task.run=function(){
print("Hello world");
}@

Is it possible? if not what would be the best way to achieve this?