m0n0wall Forum - How to access a router outside current subnet?

Hello everyone, I am new to m0n0 and just setup my m0n0wall last week.

My network layout is ---Internet---Cable modem Router---m0n0wall---workstations

The ISP provided Cable modem has router functions, and cannot be turned off. So I have to put it between m0n0wall and Internet.

The Router has limited options so I set as follows:
DHCP turned off.
LAN address: 192.168.0.1
forward all port to 192.168.0.40

The m0n0wall is set as follows:
DNS is handled by m0n0wall
DHCP on: range 192.168.1.100-200
LAN address: 192.168.1.1
WAN address: static 192.168.0.40

Since the Cable modem is not very stable, sometimes it needs to reconnect. Other than go to the machine room and physically restart it, I can do it by accessing the web management interface and reboot the modem.
So what I want to do is access the web management interface of the modem located on 192.168.0.1 from subnet 192.168.1.1/24. I unchecked the m0n0wall WAN page setting "Block private network" and try to access it by 192.168.0.1 but doesn't workout.
I guess this have something to do with the firewall/NAT settings. Please advise.

I don't want to put m0n0wall in bridge mode and let the cable modem handle routing job. I need to use some function of m0n0.

Any help is appreciated