As process and memory management is a matter of the OS itself, not the programming language you are using, maybe a more robust layer of security whithing the kernel can improve the security of your application.

Having the plain text password in memory, even for a short period of time, is not a good idea becasue it just creates a false sense of security (even a minimum window of opporunity or a strange race condition can be dangerous).

If you are using Linux (and i mean the kernel), maybe grsecurity patches can help you by improving the whole system security policies.

Your problem could be solved by using a chroot environment provided by grsecurity, which features "No attaching shared memory outside of chroot", "No kill outside of chroot", and "No ptrace outside of chroot (architecture independent)" among others.