Example for nomachine's NXClient:
Under 'desktop'
select 'unix' in the first drop down menu.
select 'custom' in the second drop down menu
click 'settings' on the right of it.
choose 'Run the following command' and insert:
gnome-session --session=2d-gnome
-or-
gnome-session --session=classic-gnome
and choose the 'New virtual desktop' option.
By default your system should have these 'sessions'
ubuntu
ubuntu-2d
2d-gnome
gnome
classic-gnome
ie, you could use gnome-session --session=ubuntu-2d for a 2d Unity session (no effects)
Session files sit under
/usr/share/gnome-session/sessions/
/usr/share/gnome-session/sessions/2d-gnome.session
/usr/share/gnome-session/sessions/ubuntu-2d.session
/usr/share/gnome-session/sessions/classic-gnome.session
/usr/share/gnome-session/sessions/gnome.session
/usr/share/gnome-session/sessions/ubuntu.session
Note:
'2d-gnome' and 'classic-gnome' look the same, I don't know if they differ anywhere in partituclar.