How to expose Custom Methods in AMImpl in ADF as REST API to consume in VBCS

Summary

Exposing existing business logic written in ADF AMImpl as RESt API's

Content

We have a requirement to re-use the existing custom business logic written in ADF AMImpl methods as REST API's to be invoked from VBCS.

The initiative is to move off from ADF app which is deployed to JCS-SX and build UI in VBCS. However customer want to leverage ADF BC objects and all custom business logic while building the UI in VBCS. 

So, we need to expose ADF BC layer as REST API's and consume them from VBCS. We know how to expose BC objects (EO , VO and any custom methods written in VO implementation classes) in ADF 12.2.1. However, we dont see an option to expose the methods written in AMImpl (AM Implementation class) as REST API.