I personally wouldn't bother feeding them at all. Feed one and a half times what you usually would for 1 week before you go away. On the day you leave, do a 50% water change and make sure all equipment is working correctly and that the filter media is clean (don't change it or you'll kill your fish, just clean it in tank water, not under the tap). Feed well and off you go on holiday.
The fish will be fine for 2 weeks with no food. Automatic feeders are not reliable and as said the blocks will just pollute your tank. Seems cruel, but really they'll be fine.
One thing, when you come back, don't just go straight back to feeding as usual. Feed 1/4 of usual amount for a few days, then raise it to 1/2 normal amount for a few days, keep increasing it gradually until feeding normally again.
This will ensure that you don't suffer any ammonia spikes as the filter won't be used to the level of waste.