Yes, ofcourse you could after consulting a medical expert. However, there is a difference between could and should. If you asked with "should", then I'd say rather consult a medical expert about that. But, since you asked if you "could", then the answer is "yes". But, still, whatever it may be "could" or "should", regarding your question, or about shoving anything up the ass, better to consult a medical expert please.
Nonetheless, I am determined along with you to make this thread the "hottest" thread of this weekend

, with or without soap and with or without shampoo

By the way, when my butt itches (though it rarely does), I apply some petroleum jelly (outer area only) : this is a common & safe relief and needs no medical expert's intervention.