I did something like this for many years, back when Amex UK had CX Gold (== oneworld Sapphire) as a platinum perk. I had my BA (blue/bronze) number on all bookings for avios/tier point collection but used the CX card to enter lounges. I only once had my FF# forcibly changed by a lounge agent who insisted it had to be that way... and I promptly changed it back on the Finnair website once I was sat down with a drink!
The technical industry terms here are FQTV and FQTS:
Originally Posted by IATA
FQTS plus FQTV are used in the event that a frequent traveller wishes to both accrue miles in one airline's scheme and also be recognised for the reason of service benefits through a different airline's scheme.