A long-range, continuous, and accessible kinetic measurement system is required for evaluating gait disorders. Although methods employing force plates are gold standard in kinetic gait analysis, their usage is often limited by their measurement range, and they are cost-prohibitive for general clinics. Instrumented insole-based gait analysis systems using accessible sensors were proposed in previous works. However, these systems rely on the use of force plates to construct models to estimate ground reaction force. In this study, a method to construct models without using force plates was developed and evaluated. Subject-specific linear least squares regression models (with bounds and linear constraints) using data from two types of single-leg standing (SLS) tasks; static SLS and voluntary weight shift during SLS were used to determine ground reaction force. Comparison of the results with force plate data for straight walking in terms of the %RMSE, which indicates estimation accuracy of the models, showed that the results were about the same accurate as the models using force plates. In addition, we found possibility that voluntary weight shift during SLS can improve estimation accuracy of models.