You hold a place in economy class, you are not a member of the airline card, then you are left with only one solution. You must be in high season and be pretty sure of the aircraft load factors. Introduce yourself last at the registration desk before the deadline. At that time, if the economy class is full, the hostess will offer you to take a next flight or upgrade you.
Also note that the crisis may be your best asset. Indeed, the economy seats are stormed and make outperform becomes simpler. For flight weight distribution of security reasons, airlines can not leave the entire front of the device (the Business Class and First Class) unoccupied. It remains to hope that fate means you.
You have 3 minutes?