Landscape LaserWriter printing is not supported using Diablo 630 emulation, just as it is not feasible on a Daisy Wheel Printer. The daisy wheel would need another print head to handle the 90 degree rotation of print.
As far as altering the IWEM to print landscape, this is theoretically possible but we know of no easy way to do this. It would involve a fair amount of PostScript programming changes to the IWEM.