I think it could be done. The TT basebar is flat like you are seeking. Im unfamiliar with the cabling/routing of the magura, but depending where you cut you would want to not be so close to the bend to kink the housings.

Keep in mind there is a routing hole/notch just near that bend. You would need to make the cut well fore or aft of this to give a strong & full section to mount your brake.

I have not seen this done however so experiment at your own risk!

I had to dremel the interior brake tube channel inside my Vision carbon base bar to make my Magura brake line fit in.