Paint on Canvas using BlendMode

I want to paint line. Blend mode is additive. Line is painted as opaque. Is it possible to paint additive?

// canvas construction
RenderTarget = UCanvasRenderTarget2D::CreateCanvasRenderTarget2D(GetWorld(), UCanvasRenderTarget2D::StaticClass(), Width, Height);
RenderTarget->OnCanvasRenderTargetUpdate.AddDynamic(this, &Rasterizer::OnRenderTargetReceiveUpdate);

// on receive update proc
FCanvasLineItem LineItem(at, bt);
LineItem.LineThickness = 10.0f;
LineItem.SetColor(FLinearColor(0.0f, 1.0f, 0.0f));
LineItem.BlendMode = ESimpleElementBlendMode::SE_BLEND_Additive;

Feature level is SM5

This is not possible according to docs:
blend mode will be disregarded for these - only SE_BLEND_Opaque is currently supported