Simple 3-way countdown timer switch
You could try something like this but I am not endorsing any particular brand:
http://www.amazon.com/Lutron-required-Single-Pole-Location-MS-OPS5M-WH/dp/B005WM3C42/ref=sr_1_1?ie=UTF8&amp;qid=1448105879&amp;sr=8-1&amp;keywords=3+way+Occupancy+switch

Apparently they do operate like you say. They still turn the light off after there is no motion for a time. 

Check the install instructions here. http://www.cesco.com/resources/027557/596670-AttachmentURL.pdf

Take a look at the 3-way wiring diagrams. You have to make a small wiring change at the mechanical 3-way when you install one of these. 

These switches do not require a neutral to operate but they do require a ground wire at the switch location. Check to make sure you have ground wires present at your switches.

Good luck