You will not be able to use Nodes in X and Y track configurations, so you will have to either set up Zones or use an InSim Circle.
A Zone is an invisible InSim Circle, which consists of X, Y placement and size (diameter in metres).
If you want to use an InSim Circle, go into SHIFT U mode, edit, Marshall, InSim Circle, then place circle on track using letter O key. Use E and W to widen or shrink as appropriate, and take a note of the circle index number. This will be needed to tell your InSim what should happen when car is driven into the circle.
Another difference between a Zone and an InSim circle, is the Zone is placed on the ground, but the InSim circle can be lowered or raised in the Z dimension.