What's the best way to handle allowance packages in Sage Construction Management?

Our situation:

Our prime contract includes (2) cost codes set aside for allowances—one called "Utility Connection Allowance" for $3,000 and another called "Contingency Allowance" for $20,000. If there is a change order for anything, they want to transfer money from the contingency allowance to cover it. Now, what I usually do is create a change order, add all of the items (each linked to their own cost code) as positive amounts, and then take the total the change order is worth and create another item with an equal negative amount and link it to the contingency allowance cost code.

For example:

A CO is created with $2,500 worth of electrical work. I would create one item in the CO for $2,500 and link to the electrical cost code. Then I would create another item for -$2,500 and link it to the contingency cost code. So, the net amount of the change order is $0, but we are now able to bill for $2,500 more electrical work.

This is just an annoying hassle that can sometimes mess up our bookkeeping if not done correctly. Does anyone have a better way of doing it?