Hi, i got exactly the same situation. i use a wifi with captive portal, that each time directs me to a welcome page, i can access to internet after inputing the use name and password like most of the public wifi where i tried in KFC, McDO, cafes...
the initial configuration doesn't accept a captive portal. the captive portal normally recognises each connection by a MAC address. if i use a normal pc to connect internet through this portal captive, it can be bypassed in another devices with the same MAC address.
so the essential step is to find the MAC address of unitiated Touchpad.
all the tool you need is
1,one touchpad of course,
2, a pc connected to internet
3,software, COMMVIEW, i use commview 5-443
with your pc, each time you connect to internet, it directs you to a welcome page, remember the welcome page url, for me wifi.free.fr. find the ip by a tool url to ip wifi.free.fr - Convert URL to IP Address | Tejji
its ip is 212.27.*.*
start commview, without any rules, start to capture packages.
at the same time, you connect touchpad with the open wifi, of coure touchpas asks you to choose another wifi source, but actually your touchpad receives datapackages from the wifi service server, ip 212.27.*.*
from the commview, you try to find from ''latest ip connections', go to the item with remote ip as 212.27.*.*, right click-hosts- by MAC, you can find two MAC address, one is your pc, the other is your touchpad.
you can confirm that MAC address in this site, a touchpad MAC is identified as a palm one MAC_Find: Vendor/Ethernet/Bluetooth MAC Address Lookup and Search
Once the mac address is identified, the following steps become easier. you change your pc MAC to touchpad mac, connect to internet. because it is a new mac, you need to input your pw and user name. once the pw ans user name is registered in public wifi server with touchpad mac address, you can connect your touchpad directly to wifi and continue the initial configuration steps.