Autodraw for Sketch
Download .zip from here, unpack and double click on AutoDraw.sketchplugin.
Doodle some stuff with Pencil tool, select shape layers and hit ctrl+shift+m (m stands for Magic). If you edited your mockup, re-select the layers and hit ctrl+shift+m once again.
Supported Sketch versions
We were testing it on Sketch 43.1, it might work on older versions too.
Sketch plugin by sympli.io
This is unofficial and experimental integration.