Going minimalistic, I think it would be possible.
Warm water, you dont need a BC, so a plastic back plate and a hog harness
If you could get DIN tanks you can save some more, Apecks 1st stage DIN 340g (12oz) Yoke 459g (16.2oz).
I think we can afford a yoke 1st stage plus primary and secondary at 708gm (25oz).
No need for an inflator hose so thats another few ounces saved.
Go wireless so no need for the SPG and hose, not sure how much you save.
1mm wet suit/rash guard, you can wear the top half so only the bottoms need to go into hand luggage, or just dive in a tea shirt and shorts.
Not sure of lightest fins or mask.
Add a safety sausage and some elastic bands to hold it on, a bonus is that it adds extra buoyancy on the surface.
Might get some strange looks when you are on the boat but should come easily under 7Kg with some spare for clothes and it will fit into the max size limits.