Go with the auto feeder, those feeding blocks make a right old mess of your water. The Eheim one is good. I tried another one, can't remember the brand but it was circular. Anyway, it was crap. Is there a Juwel auto feeder that fits in the lid?
If they're healthy and fully grown (or close enough) then they'll be OK for a week without food. Most goldfish are a bit porky anyway Fish that are a bit fragile or young fish that are still growing quickly need feeding more frequently. Small fish also need more frequent meals too. But a big, chunky goldfish will be OK for a week, if it's not a regular thing.