The only way this would work realistically is to make an actual HUGE planet. Layer gas clouds around it, increasing in denisty as you enter the "atmosphere" and radiation increasing with it. You could start outside with dense rocks that gradually disipate as you go deeper. You might even have pockets of volatile gas strewn thoughout as well. Would have to be a big planet model. In real life, liquid isn't something you find in a vacuum as a rule.
Basically it wouldsimulate diving into a gas giant.