This is a very poorly coded plugin, and a good writer should know better.
I've grepped through the code and found the
in the constructor.
However the class isn't actually assigned to a variable when defined:
And so unfortunately none of the actions can be accessed so you have no option but to modify their code. (Out of interest does anyone know how PHP handles such an instance?) To keep things simple, I'd recommend assigning the class to a variable, and then removing the hook and then re-adding it to just the admin area. To be brutally honest it shouldn't be added to any 'init' hook whatsoever, but it's probably best for compatibility reasons.
Modify last line of plugin into something like this,
And the add this to functions.php,
Hope this helps, and remember to complain to the developer!
It's very possible, and a good plugin writer should know better. The solution is not a simple one, and unless you're comfortable editing the plugin, you'll probably want to contact the author of the offending code.