How to sell backyard to developer and keep front house? Partition? Lease? JV?

[JP Leonard]

Looking for advice from experienced legal minds here 
We own a multi-family zoned lot which we originally bought intending to add a couple units in the back.
Lacking the capital and building experience to develop it ourselves, we want to offer the backyard as a "Developer Special" on the MLS.
We’d rather not risk demolishing our home at the front of the lot. It might not even be worth it at this time. We’d rather not even put it up as collateral on the construction loan.

So far I have a couple ideas how to separate the back yard for sale.
* A “voluntary partition” where buyer and seller agree that each one has exclusive rights to a part of the property. According to https://partition.uslegal.com/voluntary-partitionhttps://par...
“The co-owners may effect voluntary partition in any manner they agree upon. … Usually, a voluntary partition is effected by mutual conveyance or release executed by all owners. A written agreement is valid and need not be formalized by a deed.”
* Some kind of joint venture or common interest development. This could also be a vehicle for other investors to take a share of equity.
* One party owns the entire property and the other has a long leasehold.

(I'm told the lot can't be subdivided because the rear parcel would would need a street frontage, rather than alley access. The new California laws on backyard development, SB9 and AB1033, apply to single family zones and ADUs, not apartments in a multifamily zone. A partition agreement might allow mutual access easements to avoid the appearance of a subdivision.)