Hmmm, let's see where do I start. First you'd need a completely custom kernel for your device with the md RAID compiled in. As certainly the stock kernels do not incorporate RAID as there's no need for it on a mobile device. Of course, it goes without saying that you'd need root access to your device to accomplish this.
Once you've built a kernel with the RAID, you'd also need to incorporate the RAID management tools into the android distribution. This would probably mean figuring out the framework for cross-compilation. Then, and only then, would you be able to get into a shell, and actually create this RAID volume.
Impossible? Nope. But you have to have a decent understanding of Android architecture, Linux kernel compilation, and how to work with all of the associated debugging and recovery steps.