Different frequent flier numbers on same PNR - possible?

I've got 4 flights with different airlines coming up, all on the same PNR - starting with Qantas, then 2xQatar, and finally South African. It looks like I can only make updates to things like seat requests on the Qantas site - Qatar gives me 'view only' access, and SAA doesn't even recognise the PNR.

Now here's the question - My BAEC number is against the booking, and shows up on the Qantas MMB page. All well and good for the Qantas/Qatar flights... But I want to also have my VS FC number against the final SAA leg, so I can get my FC miles and TPs.

Anyone know if this is possible, and who I'd need to speak to to make it happen, or even if it's something I'd end up having to do at the SAA check-in later on?

thanks
RC

Easiest to do it when you check-in with SAA.

If you try and change it before your Q/Q flights have been completed there is a chance it would mess you your avios points and BA TPs