I have been going through some old (really old!) videos, and came across this one of my previous boy, Sunny. He would howl on cue. I had a little song I would sing that would set him off, or for that matter all one had to do was say to him, "You're only a dog, and that's all you'll ever be!" and he would tune up. Mattered not the position he was in at the time. Here's a short clip:
He was no slouch at yodels, either!
He was also the homeliest Basenji I have ever owned, but he made up for it with having the sweetest temperament you can imagine. :)