Land Trusts and Land Use Restriction Agreements

We have a project that is going for LEED Core and Sheel v2009 certification in a densely populated urban area and needs to pursue some form of contractual interaction with a land trust in order to achieve SSc5.1. Per addenda # 100000737, we can "donate offsite land in perpetuity, equal to 60% of the previously developed area (including the building footprint), to a land trust within the same EPA Level III Ecoregion". However, the project owner does not own any such land that could qualify under the language of this addenda. A colleague of mine has achieved SSc5 through LEED EBOM v2009 by working with GFEX (http://land.gfex.org/) and engaging in a Land Use Restriction Agreement. This involves signing a land offset contract with a third party where they agree to certain land conservation and preservation practices on a distinct piece of land for a certain length of time. Is this option available to a project pursuing SSc5.1 under LEED Core and Shell v2009? Because it appears that in the language of the addenda quoted above that a project owner must physically donate land NOT engage in a contractual agreement. Acquiring and donating 1 acre of land is not feasible for the project owner. However, engaging in a Land Use Restriction Agreement with a Land Trust or another entity is feasible. Any clarification, insight, or success stories would be greatly appreciated.