I hope the cost of printing reflects that you are doing his job for him.
What version of InDesign and OS? Your options vary.
I'm InDesign CC 2015 and OS 10.11
Find a new printer. This one doesn’t deserve your business.
I totally agree with Bob. The vast majority of printers don't use such a workflow. You'd simply provide a simple PDF of the pages, the they'd do the imposition.
What Bob said, but if that's absolutely not possible, it's probably easiest to do this with a script.
http://pdsassoc.com/downloads/Buildbooklet.zip is a very old script from Dave Saunders that does basic two-up imposition for files that have no content crossing the spine. It creates a new file, which you export with the "spreads" option ticked.
A newer script, also from Dave Saunders, handles crossovers: Dave's CS3 Booklet Script this one you export the new file without checking spreads.
IDImposer is a relatively inexpensive plugin that does fancier impositions, if you plan on doing this a lot. Overview | IDImposer
and the biggest pain method is to find a copy of the ADBPDF9.PPD file (there are a number of links for it onthe forum) and install it, then print to Postcript file using File > Print Booklet... and distill the PDF (see the comments at InDesignSecrets » Blog Archive » Acrobat’s Adobe PDF Printer Replaced in Snow Leopard)
Thanks, I'll look into this!
Full disclosure, I don't have control of the printer, the guy I work for does. So it may be like this for the foreseeable future. I'll certainly try and get him to switch.