An Applescript to export individual Omnigraffle canvases

Closed - This job posting has been filled and work has been completed.

Job Description

I use Omnigraffle Pro and I can Export individual canvases, but by default it wants to give the export the name of the document. I have to re-type the name of the canvas. I do this a hundred times a day, so it's a big waste of time.

Omnigraffle is scriptable, but I don't know enough about Applescript to do what I want it to do. I found this posting, which shows how someone did an applescript to do something similar:

But here's what I want exactly:
I want to highlight one or more canvases in Omnigraffle.
I want to activate the Applescript
One by one it will export each of the highlighted canvases to PNG, giving each PNG file the name of the canvas that's being exported.
I'd like to be able to specify in the Applescript a particular folder to save the file in (/Users/david/Documents/