You may be overcomplicating it.
Maybe just put the capital money in an account in your own name,
and arrange with the bank (or whoever) to pay the interest
into the borrower's loan account.
Before you do anything, get advice from an accountant about the tax aspects
(and by that, I mean a proper accountant, not a financial adviser,
and not one of those tax refund guys in a shopping centre pop-up).
Yes, there will be fees to pay. But given the amount of money involved,
you really should get professional advice.