There was a very similar thread a while back. At that time nobody really had first hand experience using a brake to freemount, and the consensus was that it might work, but probably wouldn’t help much.
After that thread I tried to use my brake to help mount, and found it to be more difficult. I was already freemounting with a rollback, and the brake made the uni feel too static. When I jump mount I like to hit the pedals with my weight forward so that I immediately start rolling, again a brake would trip me up.