Burning the floppy would seem to solve the problem. Lock sensitive data in RAM away from disks except for burnable floppies. I guess linux can be configured to keep sensitive data in a RAM filesystem, keeping it from being synced or flushed.
Currently, I am hacking up a prototype of an armored keysigning box using an old 386. This box signs/decodes incoming E-mail as long as the key switch is in the correct position. The key remains in /dev/ram0, and is encrypted, as well as stored in a .au file. For one of the keys, I am using a hacked des program that reads a file off a floppy for the TDES key before copying the PGP key into the ramdrive. What I plan to do is write software so that multiple floppies are needed to load the key into the RAM filesystem, and to "lock" the machine. After the key is loaded, all network daemons are killed except smail, and all gettys are killed. This makes it hard for someone locally to get to the RAM drive. If the box is rebooted, or turned off -- bye bye RAM drive.