Here is GM's project along those lines:
http://www1.eere.energy.gov/vehicles...ith_2011_o.pdf
Instead of using urea to create NH3 for NOx scrubbing, it seems that they can run brief rich periods to create HC + CO (engine out) for the TWC to convert to NH3 to "regen" the NOx trap. Funny...this is similar to what the VW 2.0L TDI does, using a NOx trap instead of a NOx catalyst.