Create low pressure around the legs, they puff up with blood which means less blood in other parts of the body. If you need a demonstration then google “penis pump”
However, I'd be quite curious if the g level is actually very low. You could have a small gently rotating section of a station.
> small gently rotating section of a station
Wouldn't work with the 4.5 m size limit of the current ISS modules, it's barely doable with a Starship-wide module, but seems totally doable with inflatables. Bigelow was designing 12m+ wide modules and that was a limitation of the rocket fairing that was launching it. With, say, Starship, the module could be much wider.
I don’t know what is the maximum difference that would be tolerable but it’s not 2x for sure.
So to get it down to single digit % you are looking at 200M+ or so in diameter.
If it’s just for sleeping and liquid pooling at the back won’t pose a health risk then if they are lying down the diameter can be much lower but you are still probably looking at 15-20M which might be possible with inflatable modules I think 3.5-4X expansion would be quite possible with the existing inflatable modules we have.