You are absolutely right that you can't tell other countries and people's what to do with their environment (and we have dramatically changed ours in our history). However, what may make a difference is the realisation that sustainable development is only possible if the vital services offered by nature are protected. Without biodiversity there would be no clean air, its largely responsible for providing clean water, removing all degradable waste, maintaining soil fertility for crops, providing renewable fuels (and combating climate change by locking away carbon dioxide). It's the sources of our food, natural fibres and timber crops, it contains the natural pharmacopeia from which most medicines are developed, and the wild genes used to improve crops, and livestock varieties to protect them from new pests and diseases. Ecosystems buffer extreme weather to protect us from floods and droughts, and the list goes on, and on.
Increasingly governments and economists are looking at the costs of all these 'free' services - if we had to pay for them it would cost the world Trillions of dollars per annum, more than the cost of climate change, and much larger than the global bank crisis. Perhaps as Governments realise what price they are paying for the neglect of their biological variety they will see they have to begin to operate differently.
So we can do lots, by helping spread awareness of the issue, and particularly by trying to reduce our own carbon and ecological footprints - this has a positive impact at home and abroad.
This is of course a major question - and no easy answers - at the heart of the solution though is recognising that the local communities, and governments need to have benefits for preserving biodiversity - and these often have to be monetised or tradable - there are many models for this, some traditional are already in place, others emerging...
All of these mechanisms have one thing in common, biodiversity is crucial infrastructure and stakeholders in maintaining it must include government and local communities, but other stakeholders including landowners and private industries have to be part of the solution too.
One of the best ways we can deal with biodiversity loss in other countries is to reduce demand for the things in our country that drive biodiversity loss. Two examples of this are meat & dairy (the production of which relies on soy feeds that are often grown on deforested land in South America) and biofuels. So some of the things you can do right away include: