Protecting Seller's Debt/Equity Ratio

Found a motivated seller who is extremely flexible. Has a good amount of equity but is willing to delay getting it. He's in no trouble in terms of the existing mortgage. He just needs to relocate because of a job change. I'm considering pitching him on alternative strategies such as a sandwich L/O or owner carryback of a large 2nd. I'd like to also pitch him on a subject to deal with him carrying back a note for much of his equity. His main concern is that his D/E ratio not cause him difficulties when he goes for a new mortgage. The sandwich L/O probably provides that kind of D/E coverage and documentation. Not sure about the carryback or subject to alternatives though. I'd appreciate any advice on how to provide him the D/E ratio protection he needs while keeping my personal $$ investment as low as possible.