Insead of focusing on Ukes wrist and "turning it over" Think of the arm as a fulcrum starting with the elbow. If you gently press down and out on his inner elbow with your none wristing grabbing hand as you turn Tenkan into KG while gently twisting the wrist in and up towards you keeping everything in your center No one with resistance can defend against the elbow pressure successfully. Call it an inner elbow Atemi if you like.. You can then "run" your none wrist grabbing hand down his lower arm as you execute KG in Omote or Ura to finish at the wrist...
In this clip Notice very carefully Nishio Shihan's brushing the elbow and inner arm of Uke into KG. As a bonus notice how the foot and hand work for Bokken and Jo are the same as empty hand...
In this clip You see how Stefan Stenudd a regular poster here interprets KG. He's had extensive experiance with Nishio Shihan Aikido and if you look carefully you'll see him making contact with and brushing the elbow washing his hand down Ukes Arm into KG.
I personally really focus a little Atemi at the elbow specifically because there is a pressure point there which comes in very handy when you get a big ol galoot of resistance from an UKE like me...LOL So my movement is a bit different but hopefully when your UKE does the big old stiff arm...You'll handle it ok.
Good Luck and now its time to go back to bed.