[Sorcery] Fire and Forget illusion

[VariousRen]

I'd like to put together an illusion spell for my Sorcerer based on the illusion advantage from powers. I'd like it to be a fire and forget spell (same as an affliction with fixed duration) where I would decide the nature of the illusion when cast and it would keep going until the duration expires or it is dispelled.

The illusion advantage doesn't have a default duration, so the fixed duration advantage doesn't help me here. Is there any way to set the duration of an advantage without a duration, such as "afflicting" the ground with an illusion?