change text frame horizontally (text area) with script?

Hi there,

I'm trying something that might be simple but am not being able to solve... When I am inside a document I created (or one that I've opened), I want to be able to change the text frame horizontally.

What I'm trying to do is exactly what I can with File > Document Setup > Text Area - Width. If I shrink this number to, say 60 mm, the result is exactly what I want. But I haven't been able to find a way of doing it via javascript...

I have tried the sample scripts for an answer or this forum or the internet, but I don't know how to do it. And I have that feeling it is quite simple... Maybe by creating a script menu action?

I'm using InCopy CS4.

thanks!