When I have a contractor's invoice, I usually do a write-in. There are some items under "Miscellaneous/Temporary, but if you use one of those you will probably have to change the price anyway. Be sure that overhead and profit on this item shows "No". If you are including tax on your estimate and it is included in the contractor's invoice, make sure the tax on the contractor's service is not added twice.
Hope this helps.
Janice R. Martin-Toll