Another esoteric tactic can be earnings through sweat equity.

Keep in mind I put in a ton of sweat equity on this project.

My preliminary thoughts would be to do a 60/40 split on the rental profits and sale, if it comes to that, where he and his partner would put in the sweat equity of managing the project and rentals while my fiancée and I maintain ownership and supply the financing.

Willing to put some sweat equity to learn about time and money cost of a project. 

Find a property with sweat equity and follow the brrrr process.

Based on how you described the proposal, your potential partner will be the investor and cover all cash considerations and you would serve as the boots on the ground/sweat equity.

It took A LOT of sweat, time, money, and stress to get ready.

Also, when doing "self-help" on a 203k, you will not get paid for the sweat equity even though the loan must include all the money that a regular contractor would charge. 

Most contractors in that area are experiencing large amounts of lagging inflation prices due to increased liability insurance, so I don't see construction costs going down anytime soon and ADU's aren't as good for appraisals as adding square footage.Is there any way to sweat equity some more value into the property?

I own 50% of the warehouse, 30% are from sweat equity, 20% my personal saving.