Take an ordinary shopping plastic bag, roll it up, insert smartly between the seat and the middle barrier. Anything that falls from your pocket will be caught by the bag instead of dropping down where it is hard to reach.
.. if i'm going to cram something between the seats.. i prefer black pipe insulation ( same materials used to grill block )
I think the Drop Stop isn't half-bad: Original Drop Stop Car Wedge - Amazing New Car Invention! We discussed it here: http://priuschat.com/forums/freds-house-pancakes/57534-coolest-invention-ever.html