I don't want to debug your simulation setup, but it looks like what you are doing is the right way to measure the gain from supply. In most cases however PSRR is defined as signal gain / gain from the supply input, so if you have 80 dB gain at DC and 1 dB gain from supply at DC you actually have 79 dB PSRR according to this definition. Because your signal gain is 79 dB more than your gain from supply. As you use the opamp in a loop this will change though.
In the end the definition of PSRR is kind of up to you, so think about your requirements and do the most relevant simulation.
In xf simulation you can put two different AC signals, so you wouldn't have to run two ac simulations (one for signal gain and one for supply gain).