Is there any way to force drawing to occur on the construction plane?
If I click at a snap point, is there any way to get curve to be at the projection of the snap point on the cplane and not on the snap point itself?
Enable the Project toggle on the toolbar with the snaps.
http://docs.mcneel.com/rhino/mac/help/en-us/index.htm#user_interface/object_snaps.htm#ProjectOsnap