Miles Plus Money Ticket Question

Hi All. We have just booked mpm tickets (X class)for a round trip to LAS. I understand that the fare does not qualify for miles and/or tier points and our booking does not carry our VF numbers. Will we still be eligible to buy an upgrade to PE from the 'My Booking' on the website prior to travel? Or does the mpm fare exclude us from this possibility? In the past, we have sometimes bought an upgrade via the website.