The way I have done it is to choose/install a printer that allows you to pick "PostScript Custom Page Size".
I've used 'MS Publisher Imagesetter' or installed the free 'Bullzip PDF Printer.
Once you select the printer and pick "PostScript Custom Page Size", you can go into advanced settings of the printer and 'edit Custom Page Size'. I choose Width of 35 inches and Height 65". That gives you a very wide canvas, especially if you choose Landscape.
-Andy