There is a motor-free spatial reasoning measure (Visual Puzzles) that comprises the other half of the Visual Spatial Index. A single substitution may be made in the FSIQ. Since only one VSI subtest contributes to the FSIQ, that would be an option for the composite score. No substitutions can be made for VSI, so both subtests would be retained at the index level. This also means BD would have to be used in the GAI. Keeping all of these substitution rules in mind, it may not be most beneficial to him to substitute VP for BD, depending on how Cd comes out. If you are attempting to capture his ability without significant fine motor confounds, subbing SS for Cd in the FSIQ probably makes more of a difference, since I would imagine Cd is far below his other scores, including BD.
If the examiner has access to it, there is also a supplement to the WISC-V, the WISC-V Integrated, that includes a motor-free version of Block Design, using multiple choice responses. Although this cannot be used as a substitute, it can provide valuable clinical and normative information regarding performance on similar tasks with and without motor demands.
Either way, a skilled clinician will be able to provide some information on his spatial ability with and without motor demands based on the primary subtests of the WISC-V.
