What about a new unit of length instead?

A light-league is the distance travelled by light in 10 billionths of a day.

1 ll = 10-10 d

It is close to the ancient celtic league.

1 ll = 2.59020683712 km

A light-league is to a mile what a mile is to a kilometer.

1 ll ≈ 1.609 mi
1 mi ≈ 1.609 km

It's a pretty cool unit.