You give the cube to the spectator, they mix it, and you take it back without ever looking. Then you pretend to solve the cube behind your back, but when you show the cube, it is not solved... it has the predefined pattern you have set in the settings.
First you have to set up your custom patterns. Make sure at least one cube is connected before you start adding/editing your custom patterns. In MAIN SETTINGS look for "Custom patterns" and tap on "Edit".
On the top of the page you will see the patterns of all 6 sides of your actual cube (that is connected). If you turn the cube, the pattern will change. Now you have to "solve" the cube to the state you want to save. When the scrreen shows the desired pattern, select a slot to save the pattern. You can store up to 6 custom patterns, each marked with a different color. Just click on the button that says "Save pattern from cube", and the pattern will be saved. You can also rename each custom pattern simply by editing the name.
If you would like to check/verify a saved pattern, tap on "Load pattern" under the specific pattern, and it will be loaded at the top of the page.
When performing, you will "activate" each pattern by turning the specific side of the cube. If you want to solve a custom pattern saved in the BLUE slot, you'll have to turn the side with the BLUE center when you give the cube to the spectator to mix.
Let's say you want to solve the cube to the pattern saved to the RED slot. Before performing, select "Solve a custom pattern" as the routine. When you give the cube to the spectator to mix, turn the RED side of the cube once, while you show them how to mix the cube. The app will then know which pattern you want to solve.
When you get the mixed cube from the spectator, wait for the countdown to finish, then follow the instructions to solve the cube to the desired state. This routine is almost identical to the simple "Solve the cube" routine in every aspect, except you will put the cube in a different state.
Just an idea: you can save the 1221 (or any other similar) stack, then you can solve the cube to that state. You will pretend that you've failed to solve the cube, but then you put the cube in a "magical solving paper bag". While doing so, you secretly solve the cube with one hand (only 4 turns)... After the paper bag "solves" the cube, the spectator can take the SOLVED cube out.