Yes, as long as you have a limited amount of users/groups it is quite simple.

Easiest is to use the Visual Studio designer and base it on PropertyString and create a Property Control for it.

Change the generated stub for the Control class to inherit from PropertySelectControlBase and you will get a nice Combo Box.

Just override SetupEditControls() and populate the list with users Membership.GetAllUsers() or RoleProvider.GetAllRoles().

protected override void SetupEditControls() {
     string username = ToString();
     foreach (MembershipUser user in Membership.GetAllUsers())
     {
         if (user.IsApproved)
         {
             ListItem item = new ListItem(user.UserName);
             item.Selected = item.Value == username;
             base.EditControl.Items.Add(item);
         }
     }
 }