Password Protecting SD-Card Data

Anyone know how data on an "Secure" Digital Card can be secured?

I'm designing an embedded arm-based board that uses a standard SD/SDHC
Card for storage, and I'd like to secure certain partitions by
password protecting them from reading/writing.

The only built-in protection I've been able to find is the SD Card's
Content Protection for Recordable Media (CPRM). Apparently the use
of this DRM with their SD Secure API, requires licensing the keys
(device, media, etc) and c2 algorithm (256 byte secret constant) from
4C LLC (IBM, Intel, Panasonic, and Toshiba.)

The SD Card Association (SDA) website shows an "Embedded SD"
specification, but haven't been able to find much more info about it
(including the spec itself, nor any card that supports it)

How best to secure data from reading/writing on an embedded platform
using whatever built-in mechanism is on the sd-card.. but with no
licensing fees? The sd-card is connected to the pc via an arm using
usb mass storage .

Thanks!