The Exclude loops collector in the Options tab lets you select the contours to be excluded from draft surfaces.

In the example shown in the following illustration, the two contours are considered a single surface because they were formed by splitting a single solid surface with a cut.

To draft only one of the contours, activate the Exclude loops collector and pre-highlight the surface edges (the loop) that you want to exclude, as shown in the next illustration.

Select the loop on the left, and it is excluded from the draft. Only the portion on the right is drafted, as shown in the following illustration.