Yes… food. The all-time best basenji motivator! How exactly did you go about your training with this? I'm interested because I take Kipawa to hospitals to cheer people up, and it would be fun to bring a few toys along and have him do this.
I clicker trained him, first to retrieve (not actually a retrieve, as I don't throw the object). Even a dog that is disinclined to pick things up, particularly things he doesn't find attractive, will learn quickly with a clicker. Initially Perry had no interest in picking up the red bone, which was one of the reasons I chose it. (he would bring back a thrown plush toy…..when it suited him! )
So, click for proximity to the bone, continue to reward successive approximations, pretty soon he sniffs it, pretty soon he starts opening his mouth, and so on until he actually picks it up. Put it on cue. I use "pick it up" as a generic for the action. Then name the object. "Pick up the red bone". With a little encouragement you may persuade him to bring it to you, if not teach "give" and backward chain it. I ask for a "service dog" retrieve......I want the object delivered into my hand, not dropped at my feet. Soon you have "bring me the red bone". Once he "gets it" start working with other objects, always naming them and working with them until he is solid on each one. Your goal is to ask for a specific object and not reward anything else......and he will try a substitution if the object you ask for is not readily visible! With a bit of practice, you can get him to hunt all over the house until he finds what you want. You can see there are practical applications for this as well.
Working right before meal time gives incentive and is a good time to practice, but obviously you can practice this with good results anytime he knows there are food rewards available. Sometimes I also toss the toys in a pile and ask for them by name. On any given day, he may nail it, but there are times when he can't be bothered and will bring me whatever is easiest or on top of the pile......which doesn't get him what he wants! Like any other behaviour, this can be overworked until the dog is sick of it, so keep it fun for him.