That's going to be tricky, because that's a long time with only pellets, you can do it, it's just not ideal, and they may accumulate fat.
If the people who can feed them are OK with handling insects, perhaps tell them exactly what brand and size to buy (take morio worms for example), and the exact number to feed every time.
When I go on holiday for longer than a week (a week without eating is fine, to be honest), I make little pots with the food pre-dosed, and a piece of paper with the days to feed where they can cross the days to be sure whether to feed or not.
If you have nobody trustworthy, then your best bet is getting them onto pellets, which shouldn't be too hard, but I'll say it a last time, it is far from the ideal source of food.
