Is it permissible to go to the mosque and stand with the worshipers while in a state of janabah, without the intention of praying, and then to perform ghusl and make up the prayer later?

What you are doing, entering the mosque while in a state of janabah (major ritual impurity) and simulating the actions of prayer without the intention of praying, is a reprehensible and forbidden act. You must repent to Allah Almighty. When the time for prayer arrives and you are in a state of janabah, you should go and perform ghusl (ritual bath), or wait until you can perform ghusl in your home. Do not pretend to be praying while in this state.