Yes modify the sp (the Last User Registered portion) to look like this:
create procedure dbo.GetOnlineUserStatistics
@PortalID int
as
-- Anonymous User Count
select count(*)
from AnonymousUsers
where PortalId = @PortalID
-- Users Online Count
select count(*)
from UsersOnline
where PortalId = @PortalID
-- Last User Registered
SELECT DisplayName,
UserID
FROM Users
WHERE UserID = (select top 1 UserId from UserPortals where PortalID = @PortalID order by UserPortalId desc)
-- Membership Count
select count(*)
from UserPortals
where PortalId = @PortalID
-- Members in last day
select count(*)
from UserPortals
where PortalId = @PortalID and CreatedDate > DateAdd(d, -1, GetDate())
-- Members day before
select count(*)
from UserPortals
where PortalId = @PortalID and CreatedDate > DateAdd(d, -2, GetDate()) and CreatedDate < DateAdd(d, -1, GetDate())
GO