You need ROM level support on a Mac. The stock ROM does one thing, boots the System Software. It would have to accommodate the fact that there may be a hibernation system image on the drive and load it if its available. Before Windows 2000 and ME added native Suspend-To-Disk support to the OS (in conjunction with ACPI), some systems supported it by adding it to the BIOS and hooking the APM suspend function. These functions tended to be limited by only supporting FAT16 HDs, and required an EXE run at boot to load a driver or set aside the hibernation file.