How to value partnership interests in a JV

Not sure if this is the right forum for this, but I've been digging and digging for the past few days doing some research to figure out how to value this thing, and I've just been coming out blank. So I thought I'd open it up and see if anyone had any recommendations. If anyone knows of a better forum to ask this question, please let me know.

We're trying to value our clients' partnership interest in a joint venture which is subject to a few conditions. For the first 5 years, our client has the option to put their interest back to the other LP for their contributed capital. Between 5 and 10 years, our client has the option to put their interest back to the other LP at a minimum for their contributed capital and for a maximum of 3x their contributed capital subject to an appraisal of certain real estate being developed by the JV. After 10 years, the other LP has the option to call our clients interest back, also subject to an appraisal.

Based on my discussions with my boss, we have a vague idea of where the value should end up but we're still stuck on how exactly to do it. At the low end, the value of our clients' interest in the JV should probably be equal to their contributed capital discounted at a risk free rate and at the high end, the value should probably be equal to 3x their contributed capital discounted at a more appropriate cost of capital. Its really the continuum in between that is giving me the most headache as well as the subject to appraisal aspect. Our client has no projections for the project and hasn't given us an idea of what the value might be in 5 or 10 years. If not for the appraisal aspect I would have thought of a simple BSOP model, but not sure its appropriate at this point.

Anyone have any recommendations?