This is silly and wrong. B5 paper is slightly smaller than A4 or American letter size paper. If a personal printer can print those common sizes, it should be able to print A5, too. A printer with A4 or letter paper would probably print the B5 page either centered or upper-left aligned on the paper. If the printer will not print the B5 page, that is the fault of the software, like the application, printer driver, or even the operating system. Updating or replacing those should enable the printer to print B5. If that doesn't work or isn't possible, then printing the B5 page to a new document, like a PDF, set up for A4 or letter paper should help. Printing that new document should work.

Must it be the first thing on the page or can it come after the site banner?