I generally recomand people who want to rehabilitate their spine to stop sitting for a while or at least minimise the amount of time they spend sitting.
Unfortunately this is not always the most practical thing to do, the majority of the activities that we do today revolve around being immobile on a chair. Some things would be down right impossible or at least socially awkward.
It would be impossible to do any long distance travelling, going out to eat, having a desk job or even doing some activities and chores around the house.
It is possible to minimise the amount of damage you do to your back when you absolutely cannot avoid sitting, although you shouldn't use this to necessarily replace all the sitting you do today with any of this techniques.
Even though it is possible to avoid the muscular imbalances to your body by using this technique, there are still other negative side effects that will affect your body like: reduce blood circulation, muscle and bone atrophy.
So here are three things you can do ranging from best to worst:
A. Squatting
It is probably the most used resting position that human use in a natural environment. Especially if your body is well aligned it is comfortable enough to be maintained for hours.
You can do almost everything you do sitting in a squat position, and squatting keeps your back absolutely straight, there is no risk of developing any muscular imbalances, that are going to deform your body.
Another trick that I use often is to squat on the platform of a chair, this will elevate of the floor allowing you to use a table and be at the same level with other people that are sitting on chairs.
You can use this at home to eat at the table with other people, it would be socially awkward to squat on the floor while everyone is sitting because you would be at a lower level, this is how I eat most of my meals.
B. Sitting on a folded towel
Some environment would require you to sit for long periods of time, and do to certain constraints it is impossible to squat.
The worst part of sitting is the pressure on your pelvis, that will make you feel uncomfortable, so inorder to alleviate that discomfort you are going to unavoidably roll your pelvis back to take the pressure of your sitting bones.
Folding a large tawole until is thick enough to lift your pelvis of the platform of the chair, but shorter than the platform of the chair living a gap behind the back rest and the towel.
Effectively supporting the weight of your body on your hamstrings rather than your glutes.
This removes most of the pressure from your pelvis eliminating the risk of rolling your pelvis and develop muscular imbalances.
This trick is useful on long flights, car rides or if you have a desk job. It allows you to sit comfortably on a chair for many hours in a row without creating any muscular imbalance.
C. Sitting on a chair without rolling your pelvis
Sitting on a folded towel it might be effective, it is a little awkward, it might get some strange looks from the people around you. Not necessarily appropriate for formal situations like business meetings, weddings or dates.
Situations in which making a great impression matters, you don't want to be the wired guy with the towel.
So the best thing to do in this situation is to sit on a chair being mindful about your tendency to roll your pelvis, and avoid doing it.
Also I would recommend not using the back rest of the chair, sit a little forward than you would normally and actually sit on your sitting bones.
The down side of this technique is that it is uncomfortable, so you won't be able to sustain it for to long, maybe an hour or two. So the next tip would be to cut your mitings a little shorter than usual before that chair fatigue sets in and your posture deteriorates.