Function to exclude columns from print

The client wants printed output that only includes the currently visible columns, which I can do with ':visible'. However they also want to exclude certain columns, irrespective of their visibility. So I need a way to exclude the columns they don't want, whilst selecting visible columns that aren't in the exclude list.

I think the only way I can do this is with a function as a column-selector. However I can't get it to work, just testing with the following:

                    {
                        extend: "print",
                        text: "Print - Results",
                        exportOptions: {
                            function(idx, data, node) {
                                return false;
                            }
                        }
                    }

As far as I can tell, the function doesn't execute when I click the print button, and all columns appear in the output.

I've tried to do a test case of this but I get a script error when I include the buttons plugin:

http://live.datatables.net/lekoduwu/1/edit?html,js,console,output

Can you either tell me what I'm doing wrong in the demo, or let me know if what I'm trying to do with the Print button is possible?

Cheers.