I haven't read the other replies so I dont know if someone else already have said this.

Before the Velius Battle I always have Ramza as Lancer
with enough JPs to jump 5 tiles. I use 'Item' as second
abilty and 'Auto Potion' as triggered ability. (make sure you have learned X-potion and not have any normal or high potions in stock, just X-potions.

With one of the other characters, I've learned 'Demi2'
from the 'Time Mage' job.
Make sure you have 'Sprint Shoes' on the character who knows Demi2 and place him/her next to Ramza in the setup. My Demi2 usually takes around 500 damage on Velius, you gotta be lucky, though, because it's not always 100% to success, normally it's around 65%.

Wizard job spell 'Flare' is also an alternative, but I strongly suggest Demi2+Sprintshoes+Ramza as Lancer.

good luck!