As the manual I have, LNAV could be armed on ground, and VNAV could not, VNAV or FLCH are both selectable on thrust reducing altitude, and it's recommended by Boeing to use VNAV.
On TAKE OFF page 2 you can input acceleration height, if doing NADP1, you can set it to 3000, so at 1500 (or anything above 400) you press VNAV, thrust reduced (sometimes increased) to CLB, but AP or FD will keeps you on V2+15~25 until 3000 as you inputted
Works on both CS757 and 767.