left foot braking will work in place of a heel toe............if you have a 3rd foot to use the clutch with.
What i would do is make some adjustment to you pedals, you can adjust them up or down a bit. Make it so its a little more even, and practice, practice, practice, and then it will become 2nd nature.
Just a note, some times you cant do a true heel-toe downshift, there just isnt enough room, as is the case in my Miata. When I heel-toe, it is more of a toe-toe, becuase I dont have enough room in there to rotate my heel to get the the pedal. So half of my foot is on the brake and the other on the gas.