i dont think you can convert a library to an init so easily, at least not without disassembling and recompiling.
it might be possible to convert libraries to shared libraries somehow, but system extensions such as init, app, thng, comd, ndrv, scri are all deeply compiled stuff.
one would think that a control panel would have been the best option for such an driver, as they can do all at once: patching the system, killing traps, providing a library, running from startup only while still offering the user to change spome settings after the boot. but from what i know it is not possible to have any kind of "translation" in a cdev, which is required for audio IO, printers and the like.
say is the sonnet software really needed to use the processor card in classic OS?