By the way, do u want the ability on a unit or hero?
Most of the spells i know give percentage bouns. So the only way I can think of is make a dummy spell that has an icon and does nothing, then once it is learned, add the Boots of Speed ability.
By the way, do u want the ability on a unit or hero?
Actually my suggestion is for hero, because only heroes can learn spells. Have you tried my method yet?
Unit - Set Movement Speed