You'd tune your first string to the "A" given by the violin, sing your little ol' flea song, and follow suit with the other three strings. Piece of cake.

If the conductor asked you to used the alternate tuning, you'd hear that A, pitch your first string a whole step lower, sing your little ol' flea song, and follow suit with the other three strings. Piece of cake.

The only problem would be finding out from the conductor whether you wanted the strings moving tuned to an A or a G. Both are used as the lowest string on the uke.