I think that the problem you are going to run into is that the front horn will raise the efficiency of the driver's output and the TL (or BR) at the back will only match the driver's original efficiency. You will end up with a very weak bass output once you factor in the baffle step response and the elevated mids and highs.

I think the only possibility would be to mate a short front loaded horn for the mids and highs and a longer bigger back loaded horn for the bass. You could arrange these two horns to acoustically "cross-over" at the same frequency. The design work would be a little tricky but I don't think it is impossible. I have been thinking about this type of two horn system a lot lately, I just need to find time to merge the two computer models I wrote for the front and back loaded horns to see what results I can achieve.

Hope that helps,

Martin