Welcome to the OptoForums! There are a few different ways to approach this, depending on what your big-picture goal might be.
In this post I wrote about an application where someone wanted to be able to switch between using real hardware and using simulated values. I explained how to use PAC Control's "Simulation" category of commands in a little logic in a chart.
But that might be more complicated than you need.
In our PAC Project Demo package (is that what you started with?) the logic for the bottling plant just points to variables (floats, ints) instead of I/O points. You'd just need to change your PAC Display project to point to the real hardware instead of the "fake" variables if/when you switch.
From within PAC Control's debugger you can change the IVAL of your non-existent digital input as shown here:
Our nifty groov product (free trial click here) provides some other interesting options too--does your project require PAC Display, or could groov work instead or in combination?
Can you tell us a bit more about what you're up to there?