I've seen the statement a number of times around here that anything you can do with the buttons, you can also do with the touchscreen.
Is this really true? Specifically, what about the STORE button? Is there a touchscreen equivalent to this button? I've looked around but haven't been able to find it…
...anything you can do with the buttons, you can also do with the touchscreen..
No, what you've seen is ... Anything you can do in the touch screen you can do with the buttons.
But just to answer the question...
Touch the gear icon upper right corner to go to UTILITY
Touch "Contents" > "Store/Save"
Set the Content Type to PERFORMANCES
Touch the box that says. "Store As New Performance" or "Overwtite Current Perf." as you desire
Give your New Performance a name.
Touch "Done"
On this screen you can view and manage all of your currently loaded USER PERFORMANCES out of the 640