there are self contained front wheel electric hub motor kits available for bicycles. the trick would be finding one small enough for a moped, or adapting the moped to a large front wheel. i think it would be nice if the electric motor were completely separate and independent of the gas motor- and putting it on the front wheel would do that.
there are also 29cc 2 cycle front wheel kits available for bikes, with an intergral gas tank. anyone for a dual engine moped (of a completely different species)?