Blue Sea Add-a-Battery Install (98 La Brisa)

1995 La Brisa with the Pro Boss 351w.

I get basics of how to install.

Motor (ECU, starter, ignition, fuel pump?) go to battery A.
Accessories (lights, stereo, bildge, blowers, etc) go to battery B.
ACR connects + of both batteries, allowing battery B to charge when battery A is above 13v.

Now, what is the easiest way of splitting the system, without rewiring the damn thing? Stock there is one heavy cable that goes to the starter solenoid and fuse block with 3 fuses on the back of the engine. Another small gauge wire goes to a relay. Is there an "easy" way to split the power on the boat, or do I have to do a bunch of rewiring?

In case anyone comes back with the same question, I ended up moving the right panel in the dash over to the "house" battery.

There is one power feed to the top circut breaker. Just replaced that feed with a new feed to the new battery and I was done. That puts the lights and stereo on the "house" battery. Bilge and blowers are still on the starter battery, but a boat guy I talked to brought up a good point. "If you pass out drunk, with your stereo blasting...you want the bilge to be on the battery that doesn't go dead".