Unfortunately, no. From
https://www.jetblue.com/help/travel-bank-credits#travel-bank-101, emphasis mine:
JetBlue travel credits can be used to pay for a JetBlue-operated flight or the airfare portion of a JetBlue Vacations package when booking on jetblue.com or the JetBlue app. Credits can't be used to pay for ancillary fees, or for travel with our partner airlines, even when booked on jetblue.com.