1) make a SCM package in COPR with Clone URL pointing to the src.fp.o fork (please, use the https:// cloning option)
2) make sure "Webhook Rebuild" checkbox is checked when you are creating the package
3) Go to settings for your package at src.fp.o and almost at the bottom in Hooks->Fedmsg section, check "Activate" checkbox and then click on "Update" button.

If your package is a main package (not a fork), then you can omit step 3.