september should be fine. I try not to move anything during august because the heat is usually jsut to intense...

but I successfully moved several clumps of LoV at the beginning of july, which gives you an idea of how hardy they are (it helps that they're shade plants, and don't have to deal with transplant shock AND the baking sun at the same time)

they grow in runners, so a garden fork is the easiest way to lift them, and they don't need to be planted more than 4-6" deep, watered in, and kept from getting too dry for the first month.

the first year they will be about what you planted. the second year, they will be half again as large a clump... the third year, they will start conspiring to take over the yard :)

and there's nothing nicer than having them take over :)