PrintDocument - Unable to change printable area via code

I'm trying to print an image to a Label printer using PrintDocument. I display the print dialog which allows me to set the page size and the Non-Printable area to have 0 size margins, and my image prints perfectly.
I don't want to have to rely on the user to change these settings each time they print, so I'm trying to set them in the code behind. I can set the page size ok, but I can't set the Non-Printable area. See code below:
        Dim doc As New Printing.PrintDocument()         AddHandler doc.PrintPage, AddressOf PrintPageHandler        &n ...