I get the problem even when disabling the first GPU. The overhead is a poor excuse for a miner that is simply outdated. His Zcash miner is even more outdated.
So ... umm ... dont use it?
The point is not to disable the first GPU. The point is that have the first GPU have enough extra memory for the OS overhead and still be able to load the DAG. Then the rest of the cards will run fine at 4GB. Disabling the first GPU does not solve the problem and misses the point entirely.