You could try painting them in a widget - splines are supported but there is not much control:
You’d run a loop on a data array. Admittedly, BPs are not great at drawing 2D, it’s not user friendly; especially considering how nicely it draws wires in the graphs, right? You’d need to expose the way the editor draws debug lines. Have a look at Rama’s Victory plugin, I believe it includes it.
On the other hand, there’s a slew of improvements coming to UMG, scroll down to the UI systems:
https://portal.productboard.com/epicgames/1-unreal-engine-public-roadmap/tabs/94-forward-looking
Chances are we’ll get a line renderer.