Update:
I got it working, it seems, atleast manually.
Basically using macshift and the codes posted here.
First steps:
use macshift to change the MAC of Wi-Fi adapter to one of the list (One that Im 100% sure hasnt been used today, 4F at the end).
use netsh wlan set hostednetwork mode=allow ssid=attwifi key=password
usenetsh wlan start hostednetwork
Share the LAN connection with the Wireless connection.
Emptied all connections on 3DS and searched for new access, attwifi, found it, set it up.
Exited settings, got the Nintendo-zone notice and saw the blue internet logo top-left. Closed the 3DS, got a streetpass 20-30 seconds later.
Next steps:
Stopped the hostednetwork service with stop command.
Used Macshift to change MAC of Wi-Fi to another unused MAC (4E at the end).
Started hostednetwork again with start command.
Opened the 3DS and waited for a good 5 minutes, stayed on Streetpass logo. Nothing happened. At this point, connection tests to the access point on the 3DS fail. Kept all settings unchanged (password).
Stopped the hostednetwork again with stop command.
This time also changed the MAC of the "Wireless Network Connection" to the same MAC as the "Wi-Fi" (4E at end).
Started the hostednetwork again.
Opened the 3DS again. BAM Internet connection and streetpass received.