Shouldn't be too hard to build. Some PVC or pipe with a dildo extender, should just about do it.
If the dildo and the pole it mounted on, can slide into a PVC pipe that is connected to the ankle spreader bar, then it can be used in self bondage.
The dildo rod should have a set of holes so that you can put a padlock in one of the holes, preventing the dildo rod from sliding back into the spreader pipe.
Slide the dildo rod into the spreader pipe, lock your ankles in the spreader bar, slide the dildo into your ass, lock a padlock in one of the many holes in the dildo rod, and enjoy.
The rod can't be retracted till the lock is removed.
Ouch.
That will rip you a new ass hole.