There is no way around this in Outlook save for creating a new email for each receipent. If you are going to be bulk sending messages you want to check you email providers policys. You could get your service cut off if they feel you are spaming.

Most companys not running their own mailserver will use something like constantcontact.com to send messages in bulk. This will also provide what your are looking for as far the user seeing only their name in the to field.