Hi Richard ,
Sorry for the delay in getting back to you. Please refer to the attached sample that demonstrates to activate HandFreeTool and you can draw your custom shape.
http://websamples.syncfusion.com/samples/Diagram.Windows/F75940/main.htmIn this sample when you click on Tool->HandFreeTool, you can draw the custom shapes.
Please let me know if this helps.
Thanks,
Nagaraj