Hi Yinon --
Gotta ask -- Have you experimented with the Genos Arpeggio feature? Genos Owner's Manual, page 57. There are guitar strumming patterns, including MegaVoice. Genos Data List, page page 74. The "Arpeggio/MegaGuitar" patterns are meant to be used with MegaVoice guitar and have various effects like fret noise or whatever.
I'm not sure if voice editing is the path to the solution. With respect to strums, there are so many factors to be controlled: what notes to play (major/minor/etc.), voicing, tempo.
At the voice level, I thought about a voice with three or four elements where each element is assigned a pitch: root, root+3rd, root+5th. The start time of each element needs to be delayed by a little bit to get the strum effect.
Of course, one needs both major and minor, but there are so many chord types! The voicing is fixed and the strum speed doesn't change with tempo. That's why an arpeggio-based approach would be more flexible.
I don't believe there is a way to create user arpeggios. (Bummer.) The only other available approach is Multipad. At least we can create new Multipads...
Hope this idea helps -- pj
P.S. Saw your reference to "pad" and maybe you already considered Multipads. Sorry.