Covert Hardware Trojan Horses (HTH) introduced by malicious attackers during the fabless manufacturing process of integrated circuits (IC) have the potential to cause malignant functions within the circuit. This article employs a Design-for-Security technique to detect any HTHs present in the circuit by inserting tri-state buffers (TSB) in the ICs that inject the internal nets with weighted logic values during the test phase. This increases the transitions in the logic values of the nets within the IC, thereby stimulating any inserted HTH circuits. The TSBs are efficiently inserted in the IC considering various circuit parameters and testability measures to bolster the transitions in logic values of the nets throughout the IC while minimising the area overhead. Simulation results show a significant increase in transitions in logic values within HTH triggers using this method, thus aiding in their detection through side-channel analysis or direct activation of the payload.