Fifteen years ago I had one done 'from the other end'.
As the paperwork was being done it was that nurse's job to persuade you that you wouldn't need more than a throat numbing spray to get through it - (since a mild anesthetic means after care and extra time spent with you
).
I consented to that, but due to my extreme 'gagging/retching' they had to halt the procedure, withdraw it, and sedate me before it could be done.
I can't imagine that 'rear end approach' would be as awful as that.