Office 365 Shared, 2 organizations

Hi, We are a MS Partner and would like to implement a Office365 Subscription, on the following scenario on a opportunity:


-A client ("CompanyA") has a Lotus Domino mail server;
-There is a affiliate company, in another location ("CompanyB"), that uses this Lotus Domino enviroment;
-CompanyA has a "companyA.local" domain (single domain);
-CompanyB has a "companyB.local" domain (single domain);
-CompanyA and CompanyB has Ipsec VPN tunnel;
-It plain to migrate and deploy Office365 with ADFS and SSO;
-Users on CompanyA and CompanyB has only one @company.com domain, shared;
-Client needs to buy just one Office365 subscription;
-There is no trust between Forests;


So, how to deploy this ADFS and SSO in this scenario?


Att,
Cezar Lins