a good headrest helps immensly for me, mine is fully adjustable mesh fabric, i can sit in this thing all day, but i cramp and cry if i have to drive for more than 2hours..., guess i just don't like car headrests.
oh and ergotron has a neoflex version for an underdesk mount, but i don't like the neoflex, that line has like nearly zero adjustability, i have a neoflex deskmount on my wifes rig and it's so un ajustable, it's just used so that there's more deskspace lol. i gave her a dual setup so the main is on a lx mount, and that adjusts really well.