This house I am in has a similar dilemma--it needs the drain pipe moved, but it is impossible to get at--it is inside the wall. The problem is that the pipe in the wall is too high. So, the plumbing with the disposal is a mess, and I am betting everything under the sink is acting as a trap (and it does stop up a couple of times per month). It occurred to me why the pipe is too high where it comes out of the wall--when these houses were built in 1940, disposals were just slowly being introduced to the market. So, the drain would only have had a trap below it originally. On top of it, the old pipes around here are galvanized steel, so they run rather poorly at times.