In the meantime, you may wish to look into recipes that call for softening or melting the butter. I have tendinitis in both arms, so I'm pretty sensitive to this; I heart my DeLonghi stand mixer but could probably mix my brownie batter by hand if I needed to, as melted butter offers very little resistance.

For any recipe that calls for creaming butter and sugar together, leave the butter on the counter for half an hour first to soften. Your wrists will thank you.