Sorry I'll be a little less vague. You can't do that because the bindings were not meant to be used together. Heel and toe pieces are engineered together, to work together and to release together. Different binding companies use different mechanisms in their bindings, therefore making release pressures/directions/processes incompatible.
In short, if you try to do that, your bindings will not release you when they should, or they might not hold you in when they should.