This is a very risky proposition because of the risk that poloinex will recover your account back to you. I would think that it would not take much more than a signed message from a withdrawal and/or deposit address for you to have full control over the account.
How? In minutes? they will recovery in minutes? And why? I'm just want to reduce my losses..
I still don't understand your position even after the explanations you have given. You have a deficit of 6.5btc already, but you want to borrow 10btc so you have a surplus of 3.5btc. Now with your account in the hands of an escrow, how do you intend to trade with it and repay the loan? And secondly, why will I give you my money when I'm not sure you can make a profit out of it since you are already owing 6.5btc? Correct me if I am wrong but that's the explanation I cash gather.