We explore the use of MoSSe Janus layers, which possess an intrinsic electric dipole caused by their out-of-plane structural asymmetry, to selectively dope graphene embedded inside a heterostructure without the need of external sources (such as electrostatic gates or chemical functionalization) in order to engineer graphene plasmons. Using the quantum-electrostatic heterostructure method, we demonstrate that through the control of the plasmon energy via the doping level and the hybridization of plasmons in different layers, we can reach graphene plasmon energies up to 0.5 eV or selectively quench certain (symmetric) modes by Landau damping. The possibility of using other Janus transition-metal dichalcogenides that could improve this effect is also investigated.