I got it to work with a little trick, using nonstandard subnet masks:
The primary router's internal LAN is set to:
- Router IP: 192.168.1.252
- Mask: 255.255.255.0
The secondary router is connected through its WAN port to the primary.
Its internal LAN configuration is set to:
- Router IP(secondary router): 192.168.1.1
- Mask: 255.255.255.128
Its WAN Configuration is set to:
- Gateway: 192.168.1.252 (The primary router)
- Mask: 255.255.255.240