PricewaterhouseCoopers (PwC) has written a report for WWF Germany entitled Sustainable Investments for Conservation – The Business Case for Biodiversity (pdf, free, but registration necessary).
The ideas is to mobilize funds held by institutional investors (in this case, in the German speaking area) for conservation through the creation of a sustainable investment holding.
Most conservation projects are too small to be of interest to institutional investors. By pooling multiple commercial projects it should be possible to create a sustainable investment holding with a portfolio that could be of interest to large investors.
The projects described in the report (ecotourism in Costa Rica and Namibia, forestry in Brazil) do not pay directly for conservation, only indirectly. And, as mentioned in previous posts, neither ecotourism nor tree-growing CO2 offsets are without problems. Still, the idea is certainly worth exploring.