Can you make a height map from BSP?

I’ll explain the question, but let me explain the problem first. There may be a better way of doing what I want.

I built a crude mountain in BSP using blocky geometry. I use this for testing gameplay and iterating quickly. I want to turn that into more natural looking mountains/hills using the Landscape builder, but I need to keep the same general heights of the BSP I made for gameplay reasons.

So I figure one way to do this is to turn the BSP into a height map, which can then be imported into the Landscape builder.

Is that possible or is there a better way to do what I’m trying to do?