In Ubuntu Yes you can do something like that.
The Dapper Drake Version is the only Distro that I am aware of that will
do it.
The USE Key needs to be named casper-cow
There is of course more to it then that
Hopefully this is enough detail
http://ubuntuforums.org/showthread.php?t=157258
It is not true RAM mostly for running LIVE on every computer. I guess in
some why it is not what you were asking however.