What happens if the value of the BTC declines below 70k? What range of time do you intend on having the loan due in? You state you are interested in an interest rate in the 6-7% range, is this per year (most likely), per month, per day (obviously no), etc?
I will be happy to post new collateral into the Escrow account, if the BTC value declines below 70K. I am looking for a 2 year term-loan, with a annual interest rate between 6-7% range. Please PM me if you have any other questions.
Just an FYI, the current market lending rate for USD is roughly 0.04% per day on Bitfinex, and after they take their fee, this works out to 0.034% per day. This works out to be ~12.4% per year, and a lender's USD would not be tied up for 2 years. Granted, it is possible that lending rates may decline from current levels in the future, so a lender may not be able to get this high of an interest rate for two years. It is also possible that a potential lender may feel more comfortable lending out USD with a specific escrow agent rather than an exchange such as Bitfinex.
Another key point is that if USD was lent out on Bitfinex (or another exchange in which customers can lend out USD), the borrower's position would be automatically liquidated once the value of the collateral falls below a certain threshold. This is less risky than the lender potentially having to wait for the borrower to deposit additional collateral. I am not sure how to overcome this issue.
I don't think the OP's story that he wants to avoid long term capital gains is unreasonable, although I have not seen evidence that he is in fact holding the claimed amount of BTC.