You are right to worry about this. Odoo's accounting onboarding documentation solves it with clearing accounts.

Opening trial balance

• Create two accounts, AR Clearing and AP Clearing, with the Current Assets type
• In your trial balance file, replace the receivable balance with AR Clearing and the payable balance with AP Clearing
• Import it from the journal entries list using the import template for miscellaneous operations, review the draft and post it

Open invoices and bills

• Import open customer invoices and vendor bills with their own import templates, and credit notes and refunds from their own lists
• Use one total line per document, with the clearing account on the line and the remaining amount due as the unit price
• The partner must match an existing contact exactly, the number must be new and its year must match the document date, and use either a due date or payment terms, not both
• Confirm the drafts in bulk from the Actions menu

Check before going live

Posting the invoices and bills moves the balances from the clearing accounts to the real receivable and payable accounts. Confirm that both clearing accounts are now balanced and that receivable and payable totals match your open item lists, then change the clearing accounts to the Off-Balance Sheet type.

Make sure your contacts exist before loading invoices, and rehearse the whole sequence in a test database first, because imports cannot be undone.