The TC is a most basic router without any fundamental ability to add resources like counting throughput.. but that is a much hard task than you realise. You simply cannot do it on a TC or any apple router for that matter.. or any other out of the box solution router by any other company. Up to this point at least. .you only solution is what you are doing.. or a special firmware called gargoyle and a router that is compatible. The best value for money (not cheapest) is Netgear WNDR3800.. simply relegate the TC to bridge and the AEx can also still work connected to the TC.. but the primary router has to be something that can run gargoyle firmware.
It is free btw.. and is dead simple to load onto that particular router.