You can put sounds on cue, you'd teach that pretty much the way you'd teach any trick, only in this case it might be easier to do it in an opportunistic way at first -- when you hear the sound, quickly pair it with the cue and reward.
OTOH, for me, the fun in the "talking" is that they do use it to communicate. They can and do learn that the sounds have a context and they can issue the sounds in context. Both of our birds are pretty good talkers, and all we've done to encourage it is to speak to them enthusiastically and consistently, and to "talk back" enthusiastically or otherwise reward sounds we like to hear. I've heard it said that they are mostly likely to learn the sounds issued with some vigor, which is why they tend to pick up swear words.
So I'd say pick some things to say to your bird periodically, and do so with enthusiasm. For example, say "Hi there!" or "What's up!" whenever you approach the cage. Not just casually, but with animation. That kind of thing.
Death Valley Scotty