I am not sure, but I imagine that you could also help out and lend your credit to this type of purchase. 

Mind you, I pulled out of the lending space back in '20.

I have a private investor who will lend his own capital for ADU financing.

Quote from @Rafael Pinho: It's brilliant when geniuses like FLW lend their talents to the noble cause of creating affordable quality.

Prosper and Lending Club also offer peer 2 peer loans, usually up to $40-$50k depending on which company you look at.

There are DSCR lending options in your personal name.

Aside all that, as others mentioned, you didn't lend enough info to give any specific answer to your specific situation.

Bottom line sub too is an advanced strategy that should only be done by Experienced investor with significant cash reserves or access to lending/like substantial LOC that already exist and can be taped at a moments notice. 

But it's hard to lend a singular #.

By doing this we qualified for a larger mortgage because we could use the rent from the other tenant to qualify and there are better lending programs when it’s “owner occupied”.