I managed to get this working for the most part.
You can start with quickset configured for AP or CPE. Then you add a virtual wireless interface for the other function. So if you start in AP mode you add a virtual wireless interface for station. Vice versa for CPE mode.
Then you can change the DHCP Server over to the AP interface if needed, ditto for DHCP Client. Be sure to add a NAT masquerade rule if needed as well.
Then you have to get the WPA profile set to connect to the internet source AP. You also need the channel set to match. I had to set the channel manually so it matched the source AP, otherwise things didn't seem to work. I was hoping if the main interface was set to auto that it would switch if required to match the virtual or vice versa, but it didn't seem to work out that way for some reason.
Unfortunately this is all a very manual process. I haven't figured out how to get it setup so that someone could just connect to the source AP in quickset and go about their business. It seems that whenever I try that I end up not being able to connect back to the wireless from my laptop.
I'll keep playing with it, but it would be nice if there was a way to make this type of setup easier for someone who wouldn't ordinarily do this sort of configuration. I'd like to be able to give these out to traveling salespeople or similar so they can easily set up in a hotel or remote site.
As it is now, I think a basic TP-Link travel router is probably easier, with the only main downside being the lack of built-in VPN functions.