Sure, you could do that by having a clipping attachment for each helmet. Probably your helmet skin has an additional slot and skin placeholder which holds the clipping attachment. A skin that doesn't need it just wouldn't have a clipping attachment in that skin placeholder.
Note that clipping attachments are relatively expensive at runtime. To help reduce the impact, try to minimize:
1) the number of clipping attachments that are active,
2) the number of vertices in the clipping attachment (eg 3 is best, else as few as possible), and
3) the number of triangles clipped, which you can see on the Metrics view. The number of triangles an attachment has is related to the number vertices (triangles == vertices / 2), so you could also say the number of vertices clipped. Region attachments have 4 vertices, 2 triangles.
