Solid Hardwood, Engineered and Laminate Flooring - hardwood floor - changing direction

I'm putting in a tongue & groove hardwood floor in a large, irregular area, so I'll have to change direction of the flooring (direction of the "tongue") once.

I have the "spline" that I'll insert in the grooved side of the flooring when I change direction, but, on the two boards which will be contacting the spline, since they are only nailed in on the tongue side, whats to stop the groove sides of each board from popping up? I was thinking about using a adhesive to hold down those boards, but there will be rosin paper under them, so that wouldn't help. My only other thought was to drill small pilot holes through the spline and boards and hammer in a finish nail at 45 degrees. Any ideas?
Thanks

Once you install the spline, you can nail through the flooring with a finish nailer, just be careful not to damage the spline. I normally don't even do that, and have no problems with the flooring. Face it, the two adjacent pieces are nailed at opposite angles, and are probably stronger than any other part of the floor.

Use your flooring nailer once the spline is inserted and the trick is, to use a scrap of flooring with the groove side engaged to your spine, as close to the nailer as possible. This keeps the spline centered, so the next row is not a chore to get engaged.