That's a good point. I've uploaded a top view with the camera sight-lines and you can see there is a triangle of space that could fit Kirk and Lenore if they squeezed in there.
When I rewatched it on DVD, it seems like the cut was abrupt from Spock and McCoy to Kirk and Lenore though. The first frames of Kirk and Lenore already show them both visible and in motion walking from that blind spot/triangle space to the right.
My thinking is that since they're already in motion and visible, they could have just finished looking out the window or some wall console and turned to continue into the observation deck. (Rather than coming around that grilled partition behind them.)