If you do not increase the temperature you would probably have to leave it in the oven for days without effecting the temper. I clamp my blades cold, but only after one complete tempering cycle, over a shim to counter bend. I use an angle iron because the ~90° will keep the bar rigid. Then I put it in the oven for a complete heating cycle. I've only had to increase the thickness of the shim once and cranking the C clamp down on it was a little hairy. I was expecting the dreaded tink with each twist but I have broken a blade yet with this method.
If that doesn't fix it after a couple of tries it's time to bite the bullet repeat the normalization a couple of times to relieve stress and then re-harden and temper the blade.
Old age and trechery will always overcome youth and ambition.