RooCode and KiloCode also have an Orchestrator mode that can create sub-tasks and you can specify which model to use for what - and since they report their results back after finishing a task (implement X, fix Y), the context of the more expensive model doesn’t get as polluted. Probably one of the most user friendly ways to do that.

A simpler approach without subtasks would be to just use the smart model for Ask/Plan/whatever mode and the dumb but cheap one for the Code one, so the smart model can review the results as well and suggest improvements or fixes.