Cheap Imposter works pretty well. It's also shareware, which means you can download a trial version first and see if you like it, then you can purchase the full version ($35) if you're satisfied. The only disadvantage was, well, I wanted to print two 8.5 x 11 onto 11 x 17, and it didn't quite show me the results in the trial version.
For some reason, you have to "zoom in" so the letter-sized PDF could fit onto the tabloid size. I started to freak out a little bit because this zoom function was not available on the free version.
Out of slight desperation, I said, what the heck, and I paid $35 to have the program. I instantly received a password to unlock all of the features, and it worked nicely.
The only thing you have to do is re-save this new file as a new PDF, then open it in Adobe Acrobat Pro and rotate the even pages so that they are face-up. If you take them as-is to Kinkos, the first printout might be upside down (this was the case for me the first time, but they willingly printed it again). To save myself the hassle, I just rotated the pages.
Of course, right after I discovered this option, I realized that Sibelius 6 imposes pages for you (grrr...I wish I knew this), but if you were to include title pages created in another word processing program, you will need to use this software. (N.B. I ended up using Sibelius's imposition option for parts; I thought this would be a better option because I didn't quite trust myself with eyeballing the zoom feature of Cheap Impostor. Of course, the whole process took me a good hour and a half. Bleck.)
This program will work for now; I believe I will eventually purchase Imposition Wizard when I get another commission or a request to rent parts for my band piece. We'll see.