In TurboTax CD/download version, you can indicate this on either the form itself or in the Easy Step interview.
Easy Step:
In the disability section of your return, there are a number of qualifying questions. On a QC return, one of these questions specifically relates to qualifying for the Quebec credit. Answer No to Do you qualify for this claim in Québec? to claim only the federal amount. Click Continue to save your selections.
Forms:
From the Forms tab at the bottom of your screen, select the form titled DTC. On the form that appears, change the answer to No.