It's good to have you here in the Intuit Community, teakdecksw,
In QuickBooks Online, upon creating a Bill you can record a deductible expense when only a percentage of work is used.
You can just add a negative value in the Bill for the deductible portion.
You may also wish to consult your accountant, to verify the transaction you'll be creating. This is to ensure that your data is in order.
If there's anything else you need help with in managing your transactions, please let me know. I'm always here to help. Have a great day!