I just learned about this trick, but I do not have any miles due to expire soon that it can save. I have ~14 rentals over the last year that do not have any miles credited toward them. Most are Hertz but 2 or 3 are Enterprise. The one closest to the 1-year cutoff was Sep 10-18 2015. Do any rentals count so long as they are directly through the Hertz website (not through e.g. Priceline), or does it matter if some are prepaid? I am willing to sell these off (PM if interested), or if there is no interest then I will call in and get a few extra miles on my own.
Thanks.