I am not sure about what you mean by "provide stress value myself at the interface". You may use the Interface Builder plugin in the Builder tools. In this case, you choose the lateral supercell for the interface structure, based on the mean interface strain value and the supercell size.
Usually, one wants to use a supercell with virtually no interface strain, but this might need to be compromised against the supercell size, which determines the computational cost of your interface calculations. So, you should adopt a supercell structure with a rather small interface strain, having in mind that you must be able to do the further calculations within a decent computational time. Also, the interface strain should not be too large to alter the physical characteristics of the interface that are relevant for your study.