I managed to start a remote gnome session following this guide.
log in a tty: Cntrl-Alt-F2
start a X session: xinit -- :1
ssh with X forwarding: ssh -X user@host
(optionally use -C for compression)
then start gnome: gnome-session
Apparently, instead of running "gnome-session", it's possible to run "kde"
Very easy, then once it's setup, use Cntrl-Alt-F7 and Cntrl-Alt-F8 to switch between you local and remote session.