Cancel the evolution during the animation by pressing the B button (or the key you use to cancel/go back).
Use a Link Stone, which can be purchased in Celadon, with the respective secondary requirement (Escavalier and Accelgor have their secondary requirement removed)
Have the desired Pokémon in the leading spot in the party, walk with them X amount of steps, and then level them up
Level up while in double battle with a partner (repeatable partner NPC is in Celadon Battle Arena once the quest is done)
dusk stone