Dark electronic spin defects in the environment of a nitrogen-vacancy (NV) center in diamond can be used to increase the size of solid-state quantum registers for applications in quantum sensing and communication. So far, these hybrid electronic spin registers have only included first-layer spins which are directly coupled to the NV, resulting in register sizes that are limited by the NV coherence time. To address this problem, we present a scalable approach to extend control to spins beyond this NV coherence limit, and we experimentally demonstrate this for a second-layer spin which is not directly sensed by the NV. We harness a first-layer spin as a probe to identify the second-layer spin using a double resonance sequence, and we achieve initialization, control and readout for the second-layer spin by performing concatenated polarization transfer across the spin chain. We also show that our method of concatenated polarization transfer can be used to control spins in deeper layers as well as multiple spins within the same layer. Together, our method and results pave the way for engineering larger quantum spin registers with the potential to advance nanoscale sensing of spin-labeled molecules and accelerate defect identification for quantum applications. Reference publication: A. Ungar, P. Cappellaro, A. Cooper, and W.K.C. Sun, Control of an environmental spin defect beyond the coherence limit of a central spin, PRX Quantum (accepted) & arXiv:2306.17155.