There would be a step anyway between the user selecting even a regular binary executable (via pressing enter after writing its name on the shell, by double-clicking on it in a desktop file manager, by running a shell script which on some line invokes it, etc) and it starting to execute (the shell or GUI would have to interpret the action and tell the OS to execute the binary).

So adding an intermediary to do a choice of executor and/or handover in between (whereas at the shell/file-manager level, or at the OS call level), but still before execution, is quite easy.