True BigH, through most projects I have reviewed this system was the most effective for a given period of time for roadways. I figure the most simi-permanent fix would be the mentioned caisson or pile method. That may price the project way out of range, and could be at risk with weather and...
Our company has dealt with many different poor sub grade sections, and has employed Pavement Recycling Systems. http://www.pavementrecycling.com/inplace/inplace.asp has a variety of applications that may meet your needs.
