Down at the Flying Saucer in San Antonio we used to pay the waitresses to go to the ice cream shop next door and make us beer floats. Guinness is adequate for this purpose, but I found Young's Double Chocolate Stout to be a much better mix.

Had some Guinness ice cream on St Pats day just past, not a fan.

Isn't a "Black Velvet" Guinness with a bubbly mix? I think you can use cider or champagne.