I assume your printer can’t print two-sided pages by itself? If Pages won’t work normally, you might just write a script to print pages 1, 3, 5, 7, 9, etc., then write a script to print pages 2, 4, 6, 8, etc. Simpler than using iPhoto, at least—but less than ideal. I can’t replicate this problem without actually printing, so I’m not sure how to fix it.