Easy: make the corporations be the ones redistributing wealth. Or the governments be the ones doing shady dystopian megacorp-style shenanigans. Or both. Sufficiently complex bureaucracy transcends corporate/governmental distinctions.
Think of the "freemium" business model, which is currently applied in a variety of games, becoming viable - or appearing to become viable - in real life. That'll be the justification for the socialism in your setting, at least: the masses are there to provide a social background for the "whales".
As for the "dystopia" part, well, not everyone fits the rules. Depending on how benevolent/competent the people who make the rules are (bureaucracy does not instantly instill either competence or benevolence), you can get as many disaffected misfits as your story requires.
For instance, Your Protagonist might have additional needs which aren't covered by the Insufficently Benevolent Megacorporation's Pre-emptive Pension Plan - say, a(n uncovered) medical condition, or an illegal (and therefore un-Pension'ed) love interest. Attempting to satisfy those needs through IBM's* normal channels just isn't working, so YP looks for someone else - and oops, IBM has a thing about loyalty.
*Despite the acronym, I do not actually have a grudge against the real-world IBM. Keeping it for now on account of hilarity.