The only way to do this without incorporating an exchange server is to switch to Microsoft Outlook and use 3rd party tools to setup a sort of public address list (like we use in exchange) to create a central repository of the address list and allow multiple connections. There are a couple products that I know will accomplish this and they have free trials for you to test with:
CodeTwo Public Fodlers
http://www.codetwo.com/public-folders/Diditbetter's Add2Outlook
http://www.diditbetter.com/add2outlook.aspxHope this helps.
MO