My answer applies only to a SPICE simulator, however, I believe it holds also for other simulator engines:
As you have on the horizontal axis in both cases the same variable, you can put both circuits together in one common simulation file with one common voltage variable.
After simulation you can simply change the x-axis and allocate a new variable which is part of your simulation circuitry (in PSpice/Probe: command "PLOT/AXIS SETTINGS/AXIS VARIABLE")