Autothrust sends a thrust command to the engine via a data bus managed by the EIU. With an EIU fault the engine relies on hard wiring from the thrust levers, so autothrust commands won’t work. You lose the autothrust on that engine and there’s no way to have autothrust on a single engine (except in engine failure or shutdown scenario).
Basically it would be a nightmare to manage with static thrust levers and frankly is difficult enough on a type with moving thrust levers. Easier with all in or all out, in my experience.