Hi Henry,
I don't think you can because .NET may not allow you to, or at least the Windows XPS driver doesn't allow custom paper size so you can't use it. I also see Epson doesn't have a .NET driver so you have to install the Windows version, I'm using Windows 7.
So here's how to. Get all of your users to create a Custom paper size using a any constant name as defined by you:
Open the report in CR 2011 SP 6 or above and set the Page Setup using your custom paper size:
Now when you open the report up it will have all of this info in the RPT files which should simply work, as long as your users are using the same printer name custom paper size name:
As you can see the drop downlist from Windows System collection has the custom paper size listed and the report now has the same saved in it.
As for how to do this "on the fly" I suggest you post to Windows forums to see if it is capable of. I don't have time to test this right now.... but test this first, update one of your reports with the custom paper size and save it. Remove the custom paper size or put test your app on another PC and see if you can set the same custom paper size on the fly. And see if CR will accept it. It should unless the paper size is cached so it may be a timing thing...
Remember, this requires CR for VS SP 8 and CR 2011 SP 6 or above.
Don
