hmmm that's a good question. i was gonna suggest adding water but you can't do that if you want to leave it out. what about natural balance rolls? i wonder if they can be left out for a few hours. although i don't see how any dog can just leave those tasty bits in a bowl to munch throughout the day. mine will eat them all in one sitting.
what about breaking up the kibble into smaller pieces? technically dogs don't need to chew their food. i know dogs that just swallow it whole
with no problems. however for this old guy grinding up the food a little bit to make it smaller might be easier for him and can be left out all day long.