The Diminishing Value calculations use the life to calculate the rate which is why the depreciation for these assets continues on past the notional life of the asset.
If you'd like to write off the balance of the assets where they have low balances following a period of depreciation based on diminishing value calculations the best way to do this is to perform a bulk reassessment on these assets and change their method to "Immediate" at the date that you want to write off the balances.
This will have the effect of reducing the NBV of these assets to 0 at that date and posting the value of the write off to the P&L in the next journal.