Two Skins, One name.

Definitely Naut Blitzcrank.

If the naming causes programming issues they can always change the name in the code. In client just make the actual champ name in the skin description all caps.

Blitz ult would have him smash the ground with the pick-axe causing a ground tremor. Naut would use electrical discharges in his abilities. Ult would have him punch the ground and send and electrical charge underground that zaps and causes the enemy champ to jump. The grab-abilities would still interact with champs the way they do without the skins.

Edit: part 2 is here http://boards.na.leagueoflegends.com/en/c/skin-champion-concepts/omzx0gsA-2-skins-1-name-part-2