The parallel kit just seems to tie together the hot and neutral legs from the two generators. That seems to 'lock step' the two generators.
I haven't tried it, but it would seem that a black box that would reverse the phase between the two generators would then cause the two generators to put out the two phases of the 220 V power line. These could then be used like the 3-wire feed into your breaker panel. Either phase plus neutral for 110 V, the two phases together for 220 V.