No, you can't use symmetry for this case, unless you're interested in common-mode S-parameters alone (which is what you would get if you used the box symmetry/H-plane symmetry feature in Sonnet).
For full general S-parameters, you need to simulate the full structure.
If you have Sonnet Professional, you could use Conformal Mesh, which really speeds up inductor simulations and other simulations with transmission lines that have high memory requirements. It can be combined with Sonnet's thick metal simulation to create pretty efficient inductor analysis.
--Max