Is borrowing with usury to purchase a home, due to the debtor's inability to repay his debt, followed by the debtor's subsequent agreement to pay the loan's interest, considered a form of aiding in usury?

It is impermissible for you to make the debtor pay the usurious interest on your behalf, or to accept that from him, because it is usury.

There is another caveat in the matter, which is that he is originally paying usurious interest.

You must repent to Allah for borrowing with usury and resolve not to return to it. Know that it is not obligatory to hasten to repay a usurious bank loan if that does not involve waiving the interest.