As long as this therapist understands that you do not have a rectum and ileal tissue is less sturdy than rectal tissue, it might be OK. I’d get it cleared by your GI first. Another thing I would be concerned about is how effective this would be. But, if it does provide some temporary relief, you’ll know the tailbone position is the cause. This is done under anesthesia sometimes, so don’t put up with more pain than you are willing to tolerate.
Let us know how it turns out.