My first thought was to start at the center and work my way out... which should be easy enough in your application I guess. Just have to insert the block using "mid between 2 points" method, likely.
Anyways, I think this might be the way to go, except there's still a hurdle left as you see in the screenshot. Assuming you're using standard 1"x4" Grating... I can't get the array to put in the next bar until there's a 4" -space- after it... which is weird... I have no clue why it does that. I'm probably just brain farting, but I'm sure someone else can get it... it's escaping me at the moment... I haven't been using Dynamic Blocks at all for a while now, unfortunately... at least not creating new ones.