To answer this question, we must look to historical sources. When one has a question involving yodeling and strange antics with animals, that means Roy Rodgers. Yes, Roy would yodel away, pining for Dale. The problem is that ... aardvarks don't pine. They are, in fact, rather stubbornly detached. It is at this point we must remember that Roy was a cowboy. Now, a stout rope might have a coercive effect on a brighter animal, spurs might work on one larger and custom boots cut just a bit tight might cause at least a bit of whimpering (even for an aardvark), but none of those things are going to get us to outright yodeling. No, Roy had certain images and urges in mind while yodeling his heart out and that brings us to an answer founded in the miracle of modern science.
[While not strictly NSFW, are you really going to click on something from this thread and hope for decency? You were warned.]
That's right! While Roy only had the memory of Dale, and perhaps a close understanding with Trigger, you can train that aardvark with: http://www.igd-usa.com/rau_ejaculator.htm. Modern technology has made it possible to juice that bull by flipping a switch and cranking a dial. Aardvarks are smaller, so run enough voltage through that thing and if the first aardvark doesn't make the right noises, there are plenty more -- digital sampling works wonders too.
Cautions:
Live performances may violate local ordinances; however, this is public yodeling we're talking about, so you probably don't care in the first place.
Aardvarks are smaller than bulls. Do not crank the dial to high until most of the notes have been recorded; PETA takes a dim view of exploding aardvarks.
Those who live in an urban setting may wish to consider the consequences of police investigating a yodeling aardvark's trainer. Consider having training devices delivered to a P.O. box.