The Thudbuster suspension seatpost doesn't try to emulate a rear suspension bike but it offers similar comfort.
Essentially, it uses a parallelogram linkage with tuneable elastomers and offers 3in of travel. Does it work? Well, yes, and our Tech Ed Steve Worland runs one and gets on well with it... However, the movement of the parallelogram in compression is down and rearward, moving you backwards away from the bar. It's effective, but most of our test team find it a bit disconcerting. We prefer telescopic sus posts because they more closely maintain the rider's relationship with the bar and cranks through the full stroke.