To create the type of investment vehicle you seem to have in mind you really need btc to be traded either on a commodity exchange or (more likely in my mind) a currency exchange.   Physical gold is not backing the various gold mimicking investment vehicles, financial gold is.   There is not enough physical gold in the world to settle all the financial contracts for gold.   Bass brother squeezes do not happen anymore because there are some many financial ways to settle your obligations.
People would not pledge their coin to allow others to receive btc returns because if you read enough of these forums, you will find that people expect their fiat back or their bitcoin back based on which one is worth more.   Go read the butterfly labs thread (it may take painful days...) but you will see that buying optionality from people that do not understand what they have given up can be very dangerous (especially when it comes time to settle the trade with the physical).
I think your best bet would be to match investments with actual buys.   Should you do those buys on an "exchange"?   Likely not, but you could do block trades with miners to supplement.    You need to remember though, a lot of miners did not invest $200MM (best guess of equipment on order, not equipment in place) to mine an asset with 150 Vol because they think the value is going down.   
Just like gold miners are not paying $800 an oz for gold claims because they think the price is going back to $250.    Liquidity will always be an interesting psych thesis in btc.