is there a way to nail hardwood floor where ceiling meets floor at 45 degree angle
Get the last rows you can nail in through the pre-drilled nail holes or with a nail gun. Toe nailing will not be critical here. The last 3 rows of any nail down floor I seen always has the last few rows surface nailed anyway. After that determine how much vertical space you have to the angled ceiling and rip a piece of material with an angle on the top to create a very short knee wall. Lay out the the rafters first to know where to nail the "knee wall". Do all the probing for the rafters if needed, behind the line that the knee wall will cover.