I have a couple of mp3s which have been encoded in forced stereo mode [no joint stereo]. Unfortunately the source material was monaural. I don't have access to the source material. Is it possible to losslessly [no re-encoding] extract one of the identical channels to save half the space [without degrading quality any further]? Any recommended applications?

In theory this is possible. But apparently no person that's skilled enough to do so bothered to code something like this -- at least to my knowledge.