As long as I have my reds, I feed them feeders only once a week or less (and fed them feeders the first time when I had them about one and a half month).
So, basically I raised mine to eat non-live foods, and they'll readily accept any food I offer them. I think shrimps, beef heart and smelt are the best food items to try out first, because most people will tell you their p's love to eat it. It usually doesn't take much persuasion to have them eat it...
As for the most healthy food source: since you only have him for a short while, you could try to get him hooked on self-made food cubes. Just blend all sorts of stuff (shrimp, fish, beefheart, blood, vitamins, veggies, pellets, basically anything you want to feed your elongatus), add a little gelatine, and freeze it into cubes. I haven't tried it myself, because I don't have a freezer at the moment, but I really want to try when I'm able to...