The buffer battery has to have it's negative connected to the engine block, assuming the house alternator isn't one with an isolated negative, otherwise the battery would never charge. It is therefore automatically connected on the negative side with the starter batt, which connects to the engine block for the starter motor return path, again assuming the starter isn't an isolated one. If I remember right, you have a Beta engine so both alternators and the starter will ground through the engine block. Theoretically, you could just use a jumper lead from positive to positive between buffer and starter battery termibals. You could even use both jump leads from positive to positive to partially get round the weedy cross section of cheapo jump leads. The connections to the B2B are irrelevent for jumping the start batt from the buffer.
