Change Irradiance map mode

Hey Jerome,

The Flythrough animation wizard is using "Multiframe incremental" as irradiance map mode, which delete the existing irradiance map and create a new one from scratch every time I render.
I wonder if it was possible to add an option to modify the mode to "Incremental add to current map".

The reason is, I often render long camera path with both quick and slow movement in it, and having to render a whole 1000 frames camera in 5 frames incremental is a huge bummer.
I'd love to be able to render one part of the camera path in 5 frames incremental, stop the render,change to 25 frames incremental and render in the same irradiance map.

Thanks!