In this paper we propose a novel clustering based multi-hop protection (referred to as CMHP) heuristic scheme to protect against single shared-risk link group (SRLG) failure in a long-reach passive optical network. We allocate the residual capacity of backup optical network units (ONUs) among the ONUs that require protection by employing bypass-based multi-hop traffic transmission through backup fibers. CMHP scheme also enables sharing of backup fibers to reduce the total number of dedicated backup fibers to be deployed between an ONU and its backup ONUs. In the study we enable a given network to be reliable by considering different reliability requirements (viz., 75%, 85% and 95%) based on the degree of reliability required by each ONU as determined by the network operator. We perform exhaustive simulation study to analyse the performance of CMHP scheme and show that CMHP scheme significantly reduces the total length of backup fiber with reference to existing scheme to protect against single SRLG failure.