I had a similar situation, about which I asked in the POUG thread
here and
here. There were some helpful replies there.
However, the ultimate outcome was inconclusive for your actual question: By the time that I'd got agreement from the passengers to have another go (long lines of communication), the POUG had actually disappeared. So I had to split the booking and do a fares rules upgrade on one booking. However, a number of days later, the non-upgraded booking showed a POUG offer again for the original flight.
The other lesson learned from that experience was that unlike what I regularly see on long-haul flights, short-haul availability can be pretty binary. My backup plan had been to do a fare rules booking from O to I in one direction. However, the flight (and others across a number of days) went straight from I9 to I0 without anything in between. Watching availability displays for a while afterwards showed this behaviour repeated on other flights. So I actually had to do a fare rules upgrade from V to R in the other direction instead.
If you split your booking and end up having to think about doing a fare rules upgrade, this is something that you might want to bear in mind.