Source: X_BANGER_X and TemjinZero
Before you start the glitch, you must have the following: (1) normal mode completed, (2) simulator completed, (3) hard mode accessible.
Play an easy Hard more mission, attaining a rank below S-rank. Repeat the same mission, but this time attain S-rank, netting you more FRS points. Repeat the mission to exploit the system!