I have done this before in the past where I used another gold card to access the lounge but miles are credited to non-status KF FFP. However, that was in SG, where I believe the agents are familiar with the rules.
When using contracted lounges, it will probably depend on what the agent has been told to do. Maybe after the entry to the lounge, you can call the SQ hotline to change the FFP back to KF?