Push Migration - How to set custom user ID?

I am trying to migrate from Ionic push alpha to beta. Please help me with the following issue :

Previously I used to register user using $ionicUser, I was able to set the user_id by my self. Now If I register user through Ionic.Auth.Signup and ID is set automatically in ionic dashboard.

So now how can set the user id myself to send push notification through user id ?

I will be grateful If I get help on this.Thanks in advance!

@Tofaelraju Were you able to find a solution to this? I am also searching for the same.

I already have user_ids generated through Asp.net Identity. It would be futile to generate the same again in Ionic. Would like to reuse the same user_ids