Precisely JT. Although you are on the mark about "None of the above" and "Abstain", I think an "Abstention" box might be a concept too far for the indifferent.
A vote for none of the above more or less covers it, while having that indefinable suggestion of humour to soften the blow of Papillon's Illiberal Act.
Phil Rigg has simply put the same thing in a slightly more sharply edged form and brings us neatly back to the BA CC IA and one of the reasons why it is such a dreadful mess. Having said that, one of the main contrary issues would not have been addressed by compulsory voting. That of CC 'writing cheques their ar$es couldn't cover' by voting for strike action and then working.
Roger.