Billable time for kit/package items

I'm hoping someone can tell me the best practice for this scenario:

We're a professional services firm, and we have several kit items that we bill to customers at a set price.  The kit/package model is an alternative to our past model where we billed by the hour, and it's intended to encompass a target amount of time we plan to spend on a certain service without "nickel and diming" the customer when we're a little over or a little under that target.

If we have employees enter their time as billable, NetSuite shows that time as unbilled, but the time may or may not add up to what we actually want to invoice for as a part of the package.  So right now, we have employees enter their time spent on that package work as "non billable."  The problem is that this throws off our reporting about the amount of our time we spend on "billable work" versus non-billable work.