If you're only going to be gone for 4 days, feed them the day you leave and don't worry about them. Fish can easily go a week or more without food. They will be fine without food. The plaster blocks will create a mess and if the filter happens to sto working, the food decaying plus the ammonia from waste will create an ammonia spike that will wipe out your tank. If the fish aren't fed, they will produce very little waste so the ammonia wouldn't be a problem.
If you feel you must feed them while you're gone, find a friend that you trust to do it. Put a normal feeding amount in a cup and set it on the tank (one for each day they will feed them). Tell them to simply pour the contents of the cup into the tank. HIDE the other food so they can't decide to feed more. If you do this, just have them feed them once on the second or third day. But as I said, the fish will be fine without food for the time you are gone.