Here's the quickest way I've found (this requires that you've set a root password):
* Edit the normal (non-recovery) grub entry, removing "quiet", "splash",and "vt_handoff". Optionally add "--verbose".
* Press Ctrl-X and let the system run through the boot process until it hangs.
* Hit SysRq-i, and type the root password to log in.
* Execute "mountall" and wait for it to block. Break it with Ctrl-C and execute it again.
On my system, I have to execute "mountall" only twice to get it to boot completely, but this may vary with the configuration. you may well need to do it more than twice, or perhaps only once.