Try to create another table (e.g. "CustGroup) with foreign key to CustCode. Then in this this new table you have two columns: "CustCode" and "Group". The "Group" column should have combination of all applicable group for that one CustCode (one customer code to many group) e.g.
Obviously you create this "CustGroup" table using from your original table e.g. using crosstable.
Then use this "Group" field in your chart.
I hope this helps.