If you can find out the system prompt format they use, I can help write a chat template to get that to work for you. I’m still uncertain about updating the official LLaMA template, though - even if llama-index expects it, it (imo) violates the principle that the chat template should preserve the format used in training.
Still, maybe it’s better than just throwing an error. Let me know if you can find the prompt format they use for a solo system message!