Most SMTP clients and servers understand a comma separated list of email addresses (Microsoft's insistence on using the semi-colon is a bastardization.) Therefore, you should be able to create a user, specifiy to forward messages, and then enter a list of addresses in the ForwardAddress field.
For example, create an account named "mylist" and in the "Forward to" field enter something like this:
user1@here.com,user2@there.com,user3@everywhere.com
I've confirmed that SME 5.6 will at least save that configuration. I have not tested to see that it is handled properly. Nor have i checked to see if SME length limits the entry, so I don't know how many addresses could be stored this way.