Question: If a Wild Magic Sorcerer were to multiclass into a level 2 Wizard of Evocation, and a fireball were to occur on a surge, would they be able to exempt themselves and 3 of their friends from the effect?

Argument for: A smart sorcerer would know what's happening, and his knowledge of Evocation magic would allow him to control the effect, if only slightly.

Argument against: Regardless of the sorcerer's skill, the surge of power from his veins is too wild to even shape, not just contain.

As far as I know, the errata doesn't cover this quandary by any means except for a mention of applying metamagic to a wild surge (you can't). Would this be a question for each DM to answer themselves or a question that has a definitive answer for all?

Answer: 
No, you can't sculpt it.
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A spell is defined on PHB 201 as

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> A spell is a discrete magical effect, a single shaping of the magical energies that suffuse the multiverse into a specific, limited expression. In casting a spell, a character carefully plucks at the invisible strands of raw magic suffusing the world, pins them in place in a particular pattern, sets them vibrating in a specific way, and releases them to unleash the desired effect
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Thus, a spell is a deliberate creation by a character or other entity.

The Evocation ability Sculpt Spells reads (emphasis mine)

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> [Y]ou can create pockets of relative safety within the effects of **your evocation spells**.
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So, the effect comes into play when you *cast a spell*.

Wild Magic Surge reads (again emphasis mine)

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> [Y]our spellcasting can unleash surges of *untamed magic*. Immediately after you cast a sorcerer spell of 1st level or higher ... create a *random magical effect*.
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And the 5e Errata (page 1) on Wild Magic Surge states

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> If a Wild Magic effect is a spell, it’s too wild to be affected by Metamagic.
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Wild surges are thus random effects, not deliberately created spells. As such, they aren't under the caster's control and aren't eligible for things like Sculpt Spell (or metamagic, for that matter).
I am going to disagree with the above statement in regards to RAW.

Yes, the Wild Magic does state that spells casted from the Wild Surge Magic table is not affected by metamagic. However, Sculpt Spell is not a metamagic ability but a wizard ability.

Also when reading spells from the Wild Magic Surge table for many of the entries it does state for many of them "You cast" and logically that certainly seems to indicate that they are your spells even if you do not have direct control over them.