CSV Import
Data import for custom metrics is available through our CSV import functionality. The primary use for CSV import will be to add historical data when creating a new metric.
You can find the CSV import on each metric's page:

Click on the "Upload CSV" link to view the form:

Your CSV file should have the following format for each row:
VALUE, PROFILE_ID, METRIC_ID, DATE
Your profile_id and metric_id can be found by clicking on the "Show API details" link on the same page above the "Upload CSV" link.