in the dialogue "Customize columns"
Click "New" button to create a new column
Enter a suitable name
Enter for "value": %custom1%
Enter for "field": %custom1%
Enable the column in the list of columns.
If you want to do the same for CUSTOM2, procede in a corresponding way with the value and field %custom2%.
Click OK.
User-defined fields do not show up in the fields list.