Exactly the reason I cannot "upgrade" to QBO!  I have more than 1500 clients with an average of at least a dozen unbilled expenses.  When I imported them to QBO, they all became active again!  "Moving them before migration" is a non-starter and would involve moving more than 18,000 charges.  Your programmers should be able to figure this out without anyone having to send you a private message to get a third party solution.  I am currently looking to leave Intuit for good (my good, not Intuit's greed).

Unbilled charges must be moved before migrating or importing files to QBO to remain a customer or vendor inactive status.