I'm sure they have software that works this out - I'd just do what you planned to do, so long as you're confident you can cover it later.
Say you would be entitled to $50/week on 0 income, but only $10/week on [x] income and you set your income at 0. You'd receive $50/week for 26 weeks, then you set your income higher and the payments would adjust down to the equivilent of $10/week for the whole year. Your annual payments should be $520, but you've already been paid $1,300, so you'd owe them the difference in the 2nd half of the year.

ETA - it really depends how much of a difference it is. You might get reduced, or you might have to pay back