As six or more people are kneeling, the Episcopal minister gives each his portion of the bread, and repeats the formula, not to each one, but once only while his hand is passing over the six.
So, I imagine, John repeated whatever form he had (and the apostles theirs) to companies, while, in rapid succession, he applied the water to them.

It is impossible to account for the performance of such incredible labor as John must have undergone, unless we adopt some such supposition as this, or confess that John's baptism was, throughout, a miracle.

But "the people said, John did no miracle." If the apostles sprinkled three thousand in this way, by companies, in one day, as they could easily have done, we can see how the same day there could be "added unto them about three thousand souls," even if "added" meant being baptized.

That the apostles had assistance in administering baptism at this early period, is not probable.

They had not yet proposed to have helpers in taking care of the poor, much less to share with them the first administration of Christian baptism.