I don't have a Genos but the following seems to work on my Tyros4, and Genos seems to have similar functions.
You could try using the 'Mix' function on the bottom of the Genos 'MIDI Multi Recording' page, after recording the volume changes for your fade in real time to an empty channel while the channel that you want to fade is playing for reference. Of course you won't hear the original channel fade at this point!
However for anything to be recorded on a channel there must be at least one note event on it, so you must include at least one note on the 'volume event' channel! You can delete it later, so you might want to make it an obvious discordant note to help you locate it later.
The volume events are inserted as CC7 Volume so do not change the MIDI velocities of individual notes. This means that if you want to, you can later filter the event list to show only CC7 event, and easily delete them all, effectively removing the 'fade'.
Once you manage to get a channel recorded with the volume changes (plus of course, a note), you could then use the 'Mix' function on the bottom of the Genos 'MIDI Multi Recording' page.
This allows you to mix together two 'source' channel to a third 'Destination' channel.
All events from the channel that you set for Source 1 are copied to the mix, but only the note events from the Source 2 channel are copied.
So if you want to apply a fade to notes on channel 1, you would set this as Source 2 for the mixing. The 'volume event' channel should be set as Source 1.
After mixing the two channels you should have the notes from original channel 1, combined with the volume fade from it's own channel.
The Mixed channel will also contain the required note from the volume fade channel, which you can now locate in Step Recorder and delete.
Finally once you are happy with the results, you can 'Delete' channel 1 and the volume event channel, 'Copy' the mixed channel to channel 1, and finally 'Delete' the volume event channel, using the functions on the bottom of the Genos 'MIDI Multi Recording' page.
You can read about the 'Mix', 'Copy' and 'Delete' functions in the section: 'Editing Channel Events of Existing Song Data', starting on page 74 of the downloadable 'Genos Reference Manual'
Regards
Ian