Maybe many people already know this, but I found it today doing some tests.

iDynamic - how to keep it enabled all the time: (for movies)

Keep ISO in manual and select the desired ISO.

For native lenses, set exposure mode in movie menu to S (shutter priority) or to A (aperture priority) or to P (program mode).

For legacy lenses, set exposure mode in movie menu to S (shutter priority) or to A (aperture priority) or to P (program mode).

Set the iDynamic to High to get one fstop lifting in shadows.

Frame the subject in a way you make the camera turn iDynamic on. If you need, frame another thing to make iDynamic turn on (a contrasty scene). With the iDynamic enabled, press the AE LOCK button. The camera will hold the iDynamic on, no matter the light changes going into the sensor. To do this you need to enable AE LOCK "HOLD" in the camera menu, so you press AE LOCK and it keeps on until you press again.

The problem for native lenses is: the AE Lock button will also lock the exposure, so the only way to get manual exposure will be using a variable nd filter.

But the great thing is: for legacy lenses the manual exposure works, because after pressing the AE Lock button it is possible to change fstop in the lens aperture ring, or using the variable nd also. And if using exposure mode S (shutter priority) it is possible to control the shutter speed, so it is complete manual exposure.

Observation 1: there are some situations when the contrast is not so high in the scene. This makes the iDynamic icon turns yellow, but there is no significant shadow lifting in the image. In this situations, when pressing the AE Lock button, the iDynamic icon will turn white. This behavior is for both native and legacy lenses. It seems that the AE Lock button keeps the iDynamic enabled (yellow icon) only when there is significant lifting in the shadows.

Observation 2: to make the camera enable the iDynamic with legacy lenses, you need to point the camera to a more contrasty and more overexposed scene than it would need for a native lens. But this is no poblem because using S exposure mode with legacy lenses you can do manual exposure after locking the iDynamic on. But there are moments that even with the camera pointed to a contrast scene the iDynamic does not get enabled. Maybe the Dandelion chip can be the solution to make the camera to "think" there is a native lens in the system to make iDynamic enable easy as it does with native lenses.