Swizzle UIApplication.sendEvent to intercept the pencil touches sent to the WKWebView’s gestures and redirect them to an overlaid, disabled PKCanvasView’s intercepted gestures; call the original gestures’ touchesEnded. Cache the gestures in a weakToWeak NSMapTable for successive events. contentSize, contentOffset, and zoomScale syncing is trivial.

I have it working even without swizzling using custom drawing engines. The issue lies within the dynamic and changing nature of the web and cross-device/size display unless you imagined it as one-off raster drawing.