you can make your own standard bp spline but you will be missing out on some features like control clicking with landscape spline and some terrain falloff settings.
After alot of searching back and forth i found this
basically make your own intersection mesh and use this code in the construction script to snap them together. You can’t transform the landscape spline though which is lame.
your other option is to use the landscape blueprint brushes and program them with a solver or spline point options to select your intersection mesh