My routing is:
FRA-LHR (BA) LHR-MAD (IB/BA) MAD-LHR (IB) and LHR-FRA
I remember from previous flights from FRA-LHR that I was offered to upgrade for something like 69 EUR per leg and happily took that as I did not have any status with OW and could have spent some time in the lounge.
The most "interesting" flight is LHR-MAD as it is operated by A346 and upgrading this would give me a at least a nice seat. But this one seems to be the most difficult one as IB does not offer me to bid for the upgrade and BA won´t be able to offer me AUP.