Yes, it should be possible.
You create three networks in the W8970 device. First network is the one hosted by the AP station on this router, and includes three Ethernet ports. Second network is the wired connection to the TL-R470 device using the last port. Third network is the wireless connection from the external USB STA to the TL-R470.
Although this setup is possible in theory and in practice, it's feasibility is in question. If your intention is to gain more throughput, then the 150 Mbps wireless link provided by the external wireless device pales in comparison to the transfer speeds through the wired Gigabit Ethernet link. It's like having a 60 ton truck and trying to "augment" it by adding a 1 ton trailer.
So, care to explain what the purpose of such a setup is?