Frontier AI models pose increasing risks to public safety and international security, creating a pressing need for AI developers to provide credible guarantees about their development activities without compromising proprietary information. We propose Flexible Hardware-Enabled Guarantees (flexHEG), a system integrated with AI accelerator hardware to enable verifiable claims about compute usage in AI development. The flexHEG system consists of two primary components: an auditable Guarantee Processor that monitors accelerator usage and verifies compliance with specified rules, and a Secure Enclosure that provides physical tamper protection. In this second report of a three part series, we analyze technical implementation options ranging from firmware modifications to custom hardware approaches, with focus on an "Interlock" design that provides the Guarantee Processor direct access to accelerator data paths. Our proposed architecture could support various guarantee types, from basic usage auditing to sophisticated automated verification. This work establishes technical foundations for hardware-based AI governance mechanisms that could address emerging regulatory and international security needs in frontier AI development.