Have you thought of using a special document type and excluding if from financials unless needed? Or maybe a separate ledger for these entries that can be added to the financials when needed?

Yes we had suggested using the special document type as a workaround.

Create a new company with the same set up as the existing one apart from the fact that the calendar will be a single period for the fiscal year.

Post your year end adjustments in this company.

Set up a company group that includes both companies.

Use the group in your enquiries and you then have the data for your statutory accounts.

This set up is not ideal but has some useful side effects in that you can limit access to that company and also you can do a year end and close in  your active company while still keeping the period 13 company open awaiting postings. In some countries that can be up to 8 or 9 months after year end.