The below takes a bit more upfront effort but will pay off if you’re watching him for a couple days or more. It’s all about building up a trusting relationship. This is my best suggestion having been around many types of animals and dogs my whole life, if you end up trying it genuinely curious if it works for you!

Go outside and just walk around, minding your own business. Don’t try to call the dog. The goal is to let him get used to you being around. Feel free to walk the perimeter of the enclosure or just stay in an area and walk along a square/triangle. Eventually he will start to show interest in you walking around in “his” space, so watch for him looking your direction. Say “good boy” when he looks and turn around and quickly walk the other direction. Do this a few times until it seems you have a back and forth communication somewhat and he’s showing interest in your movement. Now start dropping treats on the ground as you walk and make sure he notices. Give him plenty of space to pick them up. Next, crouch down, turned 45 degrees away from him looking to the side and gently throw a treat his direction. Let him approach to take a treat from your hand. Don’t pet him this first session. After this try to walk inside and ask him to come in.