I too have had good results with the baking soda technique, albeit in small areas (like a car), in an open container, giving it a shake every so-often to expose the fresh stuff to the atmosphere.
You just need to try and maximise the surface area of the NaHCO₃ as much as you can, rather than having a thick layer where the circulating air can't get to. A lot of those "Shake'n'Vac" type products usually contain a high proportion of Calcium Carbonate (and some pretty smelling stuff), which act in a similar way, however I don't think I'd be putting either directly onto the carpet for long periods, because both are hygroscopic and could damage certain surfaces/products.