I'd hammer the last rows in. There is a sort of s-shaped tool available that fits into t&g flooring and lets you hit it with a hammer to tighten them up along the final rows. I don't know what it is called, though. As for fastening the last rows, I would face nail them with finish nails, countersink them, and use a matching wood filler in the holes. I don't think you have any alternative. Anyone?