In PSPICE plotting is not based on programming like that in MATLAB. In fact, the plotting is based on the set of variables that can be selected for x and y axis. The problem, however, is that if you want to plot two curves with different ranges of x axis variables.  I spent quite a time on solving this issue. Although I did not reach where I wanted to land, however, i found one solution but first, let me introduce you to the circuit i wanted to simulate.
The figure above shows two PV cells connected in series with each other. The combined output is taken from the node 3 and 5. I want to draw the I-V curves of both the cells as well as their combined output. However, in order to do so if I select the x axis as the voltage V3 the I-V curve for the individual cells is compromised and if I select the x axis as V3-V1 then the I-V curve of combined cells is compromised. To solve this I selected two plots and unsynchronized their x axis as shown in the figure below. To unsyncronize the x axis click on plot > unsynchronize x axis.


The next challenge is to plot them on one plot.