Azure AD B2C KMSI - Built in policies

Hi Microsoft Azure Team,

I have an .NET Core 2 solution with 2 Projects. 1. SPA 2. Web API (Both will be hosted into Azure Web Apps later)

I am using Azure AD B2C with MSAL.js  to login to the SPA and call the authenticated endpoints in the Web API project.

I would be converting the SPA to a Progressive Web App later. 

I would like to have KMSI functionality in my app. I am currently using Built In policies for the Azure AD B2C. I found in an article that KMSI is possible only through Custom Policies.

https://docs.microsoft.com/en-us/azure/active-directory-b2c/active-directory-b2c-reference-kmsi-custom

I have to now change my built in policies to custom. Is there any way to achieve KMSI through built in policies?  Kindly advice.