Eh.. If you learned some programming, you could help ctrbootmanager to handle such things.
GW payload is encrypted with AES-CBC, which key is known, and not a plain binary.
That's why it doesn't support auto-boot via themehax, currently.
If you could add the decryption methods to ctrbootmanager, then key handling, you would not be far away from your hope.
However some of us are all lazy guys, and don't want to add a feature which he can not tell working or not easily.
That's gateway's duty, not personal devs, nor its users - yup but users care about it.