Fish can easily go a week without food. Many on this forum have done it. I would definitely stay away from the block feeders. They are mostly plaster or whatever they are made from and very little food. All they really do is mess up the water. Automatic feeders can be risky as they could malfunction and dump too much food in causing an ammonia spike.
If you feel you need to feed them, find someone that can do it for you and simply put a normal feeding in a cup, one for each day they are going to feed them. All they have to do is come over and pour the contents of a cup into the tank. The next time, they pour in the second cup. Just hide the food so they can't decide to feed more because they don't think what is in the cup is enough.
Another side benefit to not feeding is that no food means they will produce very little waste. So if the filter should happen to go out or you have an extended power outage, the ammonia build up will be minimal.