Unfortunately, Beta-1 agonism from clen at higher doses is responsible for much of its effects. It is only truly selective for B-2 at very low doses.
So by taking propranolol, you're blocking all the B-1 activity (which is very effective for weight loss) and relying on the B-2 effects, which are milder. I'm not crazy about the idea of taking 2 potent drugs to mostly cancel each other out (taking a low dose of clen would be simpler and more fool-proof), but I'll admit that the idea is interesting and has its merits (mostly because it should be blood pressure friendly, since you're cancelling out all adrenergic pressor activity).