You could take the Crossblooded archetype for Draconic and Orc, getting +2 dmg per die rolled...
But, you are losing out on BAB, on an already 3/4 BAB build... a build that is going to want to hit stuff.
Yeah, I'd also recommend taking the Crossblooded Sorc archetype and getting Draconic (Fire) and Orc for the +2 per die rolled whenever you cast a fire spell, and +1 per die rolled for everything else, and you can make up for the lost BAB by taking Heirloom Weapon trait for a +1 trait bonus and maybe even pick up Weapon Focus as your lvl 1 feat.
You can do it, I'm sure you'll do fine. Magi don't really have trouble hitting stuff despite being 3/4 BAB. Of course theybdon't really have trouble doing damage either, so you don't really need +1 (or +2) damage per die.
If we look at Shocking Grasp, the average damage at 10th level is 35, or 70 on a crit. With a Keen Scimitar it actually averages out at ~45 damage per cast (because you're much more likely to crit).
If you went for a dip in Draconic or Orc Bloodline for +1 per die the average damage would be 45, or 90 on a crit. Factoring crits in it would be ~58 per cast.
If you went Crossblooded for +2 damage per die it would be 55 average, or 110 on a crit. That's ~71 average factoring in crits.
Now that seems like a lot, you've gone from ~45 to ~71, that's a ~60% increase. But by this point you should be making ~4 weapon attacks per round, so your spell damage should only be ~1/2 your damage output . By taking a dip you delay everything (including BAB and caster level) by 1, so that reduces your effective in a number of small ways. By going Crossblooded you also add -2 on Will Saves - not something the Magus is usually had at, but still a penalty.
So it's doable, it'll add a noticeable amount of spell damage but comes with a number of small penalties. Totally up to you.
EDIT: I should clarify: These are Intensified Shocking Grasps (level 2 spell), and you get to 10d6 at character level 11 (Magus-10/Sorcerer-1). You can decrease the spell level and increase your caster level using traits/feats, but that's the baseline.
Yeah actually, going Blue Dragon for bloodline would give you +2 to Lightning, and Shocking Grasp is a bread n butter spell for Magus.
I would lose only +1 BAB when taking 1 Level as sorcerer. all other levels would be magus. But it sounds crazy to gain +1 (or +2 crossblooded) for each die. Just think of Wizard (Evoker) taking 1 Level Sorcerer...gaining +1 Damage per die and the + 1/2 Level on damage also...
Just to clarify you'd lose 1 BAB, delay all your saves by 1 level, lose ~1hp, lose 1 caster level, delay access to Magus Arcana, Arcane Pool weapon upgrades, new spell levels and any other class features you care about.
You'd gain +2 damage per die on all spells of the correct damage type, +1 per die on all other damage spells and gain access to a good number of Wands (without needing UMD) and a few more cantrips. You might evem gain a class skill or 2.
There is a cost to this, but also a benefit. I think it' a pretty good dip.