Thank you for the various answers and suggestions. These are really addressed to my first problem - the incisional hernia. I have tried various cinching devices without any degree of success, and I believe I know the reason why. With all the engineering talent here, perhaps someone will have a further suggestion or at least shoot down my own take on the problem.
Most people seeking to reduce their waist line at least have an intact abdominal wall to sustain intra-abdominal pressures which can be surprisingly high. While the anatomical girdle formed by the abdominal wall may be larger than desired, it is at least sustaining the intra-abdominal pressures, and any tension applied by a cincher is additional. With an incisional hernia however the girdle is broken, and therefore any cincher must overcome the intra-abdominal pressure to close the hernia (probably approaching four inches at its widest) and restore the girdle before any useful pressure can be applied. This entails an uncomfortable or even injurious degree of compression. Surgical correction is problematic and painful because of the high stresses that must be sustained by the repair, and unfavourable outcomes are common. It is clear that at least my own surgeon would rather let well alone, and certainly I am not keen on the idea of fairly major and problematic surgery. A concern of mine is that the lack of control of intra-abdominal pressure may be a risk factor for the recurrence of a splenic flexure volvulus.
It occurs to me that intra-abdominal pressure would best be counterbalanced by some form of inflatable belt, but this would seemingly just substitute one form of 'spare tire' by another.