In Illustrator, it's easy to make a bezier curve transition to a corner point so you get a point with only one bezier handle.
I haven't been able to do this in AE. I can hold down Option with the Convert Vertex Tool to break the handles of a bezier. But I haven't figured out how to get a corner point transition. I've been dragging the broken bezier handle back to the vertex point, so its length is as close to zero as I can make it. But it's not perfect.
Nope, can't do. But there may be some script out there that zeros the tangent handles perfectly, so check AEnhancers and AEScripts.