Just ask lenders from your locality and make your BTC investment as collateral, maybe they will consider it. But I was thinking deeply about why you need to borrow ETH which in fact you can directly buy BTC in any exchange. However, talking about borrowing money was not advisable but of course, if you don't have any option in order to have capital then that might push you to do that. But the problem is if there is someone or any lending institution that will help you.