Embark deep ocean only

Is there a promotion or some code I can use that allows a unit (helicopter) fly just over coastal tiles and land, but embark when it hits deep ocean?

I removed all embarkation promotions from the Helicopter Unit Combat, but they are restricted to just land and coast.

I'm not sure how to make a new promotion giving that ability to only embark on deep ocean tiles.

If it matters I have custom unit classes, and it didn't matter since the combat class is all helicopter.

The bad news is it requires extensive DLL modding

The good news is I've already done it - see the last para of the description of this mod

definitely food for though man.. when are the devs just gonna incorporate your DLL changes into the core game dll.. lol