It's really not a good idea, so many things could go wrong. But if you must, here are some things you can do.
Leave a water dish filled with enough water to last 4 days.
Get a timer* you need your beardie to have a day and night cycle. These can be a little expensive, around $30. But it's necessary.
Leave lots of feeders in a dish. Remember, this has to last 4 days. I use dubias, they can't climb out of glass dishes.
My beardie won't eat commercial bearded dragon food and he shouldn't because there's no nutrition value. But in your case, try leaving some commercial BD food around his cage in case the feeders don't last him the whole 4 days.
Give some greens the first day you leave. Whatever he doesn't eat won't be good the next day so only leave enough greens for the first day. Don't forget to dust!
Also try leaving one of your worn shirts in his cage. He'll still have your scent with him while you're gone.
