The easiest way around that is a pre-qual letter for your buyer.
I don’t recommend faking a proof of fund by using hard money. If the hard money lender is willing to fund, then they can place the $$ in escrow. You can open escrow at the same time that you submit the ss package.
It is a disservice to the distressed home seller if the ss is approved and the buyer cannot close due to lack of funding. Secure the funding for real before submitting a ss package.