IIRC, canonically, the ComStar used weird master-slave combination for all their units, which seems to be strictly illegal (at least i interpreted things being as each unit having both). In practice, we've never actually seen them use standard C3 systems. So perhaps they quickly figured out they can't actually use C3 system practically and proceeded to develop C3i system.
You can actually get away with two masters and four slaves. Or, well, two 'Mechs with master computers, one just needs to carry two of them...
Personally, i'd just use two partial networks. Two "light" lances, with one master and two slaves each, and just live with the fact the networks don't interface.