Your goal should be to gain trust, respect and establish leadership and to that end you mention several methods you use on the mustang:
A. Hand feeding your horse = when you hand feed a horse in his mind you are indicating that he is the leader because he is in fact taking your food. Inside I suggest you put the treat in a bucket on the ground.
B. Clinton Anderson does round pen but if you watch him and in fact "Buck" Buchanan does not round pen anymore. The trainers that do use the round pen technique normally round pen until the mustang maintains direction, turns in and focuses on them with to eyes. Then they use a lariat, rope the horse and continue basically round penning in both directions till they can touch, rub and finally halter the horse. Then they continue the ground training in hand usually beginning with yielding hind quarters. Unless you are experienced using a lariat with soft hands I do not recommend you try this technique.
Although Round Penning and JoinUp can be useful it is not be all. End all. Really like baking a cake there are many recipes to train a horse; the trick is to find the one that works for your horse.
So far you have made some progress where he at least comes to you but I think he is only coming to you to get out of work and at this point does not trust you. If you continue running your horse around in a circle you will in fact teach him to not stand still. Bottom line is you must focus on gaining the horses trust and being able to touch, brush and halter the mustang. Then you can begin seriously training your mustang.