Sum repeating rows as one

If it's just for aesthetics in a table, have you tried changing the field in the table to show as the 'average' rather than the 'sum'?  That way every day will still show 100, but your totals will also reflect 100 as the average of all the repeated goal amounts.

To work with this goal amount independently, say in a DAX measure, the goal should be removed from the table that holds the daily rows (since 100 doesn’t really mean anything to a particular day), and listed separately in to its own 'dimension' table', one row for just Joe, with a goal of 100 (along with the other customers and goals).

Relating these two tables together on customer# will let you work with the goal in a DAX Calculate() measure if need be.  You'll be able to use the related goal against any other aggregation from your detail log. i.e. if you keep track daily of each pound lost, you could sum the total pounds lost (from the detail table), then compare them to the goal of 100 from the goal table. 

Hope this helps.