Hm. That does seem surprisingly difficult in a graphics layer. It would be nice if the graphics sketch could use some of the standard drawing tools, like making a segment parallel / perpendicular to another.
Honestly, we don't use graphics layers much. We have some generic "annotation / sketch" feature layers that we use to add points, lines, and polygons to a map. We prefer these precisely for this sort of situation where we need the advanced editing tools.
- Josh Carlson
Kendall County GIS