Just a quick short post. Even shorter: use the toram boot parameter.
I was looking for an option to copy the contents of the live CD into RAM during boot and was looking throught the source of the casper script (the one that mounts the stuffs to have a working root or /cdrom for Ubuntu), when I saw a function called copy_live_to().
This function does exactly what I was looking for – copies the contents of the live CD or the media it was about to use as root (an NFS mount in my case, see the previous post) and releases it – all you need to do is adding the toram boot paramter.
After it has been done, the original medium can be removed – i.e. the Live CD can be ejected (in theory, I have not tried it yet).