Umm. This is going to sound really stupid, but can't you just subtract the morph values of the base from the final morph prior to distribution? I mean, take Vicky, turn the 'final morph' to 1.0 and then set heart to -1 and round to 1 (inverting the values of the base morph). Then export the result as 'distributable final morph' - what you have left is what is your own additions. You could add a note in the readme saying 'thumbnail image generated with heart set to 1 and round to -1' or somesuch.