Do you know what is causing the problem? I have dealt with sciatic issues for years, and in my case, it all results from a rotated sacroiliac joint. If a rotated joint is the issue, it may be amenable to corrective manipulation into its proper orientation. I have learned how to re-position it myself, but I can't help you without knowing for certain whether that is your issue, and in which direction it is rotated.
If you have not had the condition diagnosed by a good physiotherapist, I recommend seeing what one has to say. Good luck with it mate.