Row Level Security RLS with external users. Can't set their role until after they accept

Our company is using Row Level Security RLS with external users to filter the data. We can't set their role until after they accept the invitation, which means after they accept, they can't see the report data until the role is set. Unfortunately, all the users will accept at different times, so there doesnt seem to be a way to setup their roles until after they accept. 

Is there a way to setup the role on the gateway before they accept. We are using Microsoft 365 for our internal logins/email. 

I am not sure what our clients use, it suppose it would vary from client to client.