I looked through the threads that were listed here and did not see any discussion of storing keys in memory.
In this system you start a daemon that requires a password. That daemon can then be used to retrieve the password for the database. There are 2 commonly used examples of this approach, ssh-agent and gpg-agent and it is possible that you could use gpg-agent.
Certainly this is not totally safe, but much safer than having the password on the harddisk. The password itself is only in memory for a short time and the key is sitting at some (hopefully) unknown place in memory.

The down side is -- Just like if a password protected ssl key with apache -- you have to type in a password each time the daemon is started.