Thanks for the link. Unfortunately it doesn't seem to work on my setup either.
Created a FreeDOS boot USB key, dumped HDDERASE.EXE on it and then ran it but it just hung as it was enumerating all the PATA devices. The command prompt never showed up.
Oh well, maybe OSX's secure erase function will work?
Edit: Just tried doing it via hdparm from GParted but my STEC is in a "frozen" state so it won't let me proceed. Ack. I guess I can try hot swapping the STEC to see if that will unfreeze it. Ugh. What a pain!