Exchange 2010 - Bulk Create Secondary Email Addresses for Dist-Groups and Mail Contacts

Hi, I have 500 Distribution Groups and 700 Mail Contacts in my Exchange 2010 Env't

we are going through a company merger and require us to add in a Secondary Email Address to the above.  We cannot use Email Address Policies for a few reasons, which I won't get into, so we are either doing this manually 1x1 or if can powershell it?  I am a newbie to powershell so would requite good step by steps please

Thanks,