Comsol 4.3b is now installed under /cvs/cds/caltech/apps/linux64/COMSOL43b. I've left the existing Comsol 4.2 installation alone; according to the Comsol installation guide [PDF], it is unaffected by the new install. On megatron I've made a symlink so that you can call comsol in bash to start Comsol 4.3b.
The first time I ran comsol server, it asked me to choose a username/password combo, so I made it the same as the combo used to log on to megatron.
Edit: I've also added a ~/.screenrc on megatron (based on this Stackoverflow answer) so that I don't constantly go nuts trying to figure out if I'm already inside a screen session.