I don't have a Genos so I can't confirm that this is actually implemented in the current firmware, but starting on page 139 of the Reference Manual there is a list of functions that can be assigned to a foot pedal or an external controller such as MFC-10, via the External Controller template.
The last but one item in the section of the list for 'Functions that Respond to On/Off Input' (ie. the MFC-10 foot switch buttons) is:
"Multi Pad 1–4, Stop: Same as the MULTI PAD CONTROL [1]–[4] and [STOP] buttons." (page 141)
These functions were included as individual entries in the equivalent function list for the template in the Tyros models, but in Genos it looks as if they have been 'bundled' together in a single entry in the main function list. Presumably selecting this opens another window containing the individual options.
I assume that if you select the 'note/switch' that you want to use in the relevant Genos screen, then scroll down to the bottom (to page 5?) of the list of functions and touch this entry, a window containing the various options to start each individual MP, and stop all MP's playing will open and you can select the specific function for this switch/note.
I saw in another post, albeit about a different function, where after touching the screen to open the option list, you could only scroll through the options using the 'data wheel'. Could this list be similar?
As I said I can't confirm this personally, and there seem to be some inconsistencies between what the manuals say and what users are actually finding in the current firmware version, so this function may not actually be available to select yet!
Personally I am content to wait until Yamaha get their act together and sort out the
bugs sorry, of course I meant 'anomalies' in the Genos OS before I even look at one!
Regards
Ian