I think the suiciding with someone rescued thing only works in FE6, I tried doing it with Tana in 5x in reverse recruitment since she'd come back anyway, but the unit she was carrying lost her move.
you can technically two turn if Vanessa survives like 6 enemies including an archer while carrying Seth, but the odds are pretty much less than zero, especially in 0%
actually you might be able to use the torch glitch, but that's pretty lame.
edit: apparently I did it in my last playthough, maybe I found something different, idk if I still have the videos after my computer crashed though
edit edit: Its definately possible and kind of reliable actually, Vanessa with some levels isn't oneshotted by the archer, and she only gets attacked by two enemies. In 0% it might be possible, but I think people would get clogged up and Vanessa wouldn't be able to dump Seth by the boss due to enemies in the way. I guess its kind of reliable when Franz and Vanessa have really good stats.