Hi Hanu,
as far as I know using the standard document flow (e.g. as you can see in the OIF of a sales order) is not possible for custom business objects.
However, there might be a way to achieve more transparency into predecessing documents for your custom transaction. If you have a reference (e.g. an association, a field containing the ID or UUID) to the sales order in your custom transaction, you could display the ID of the sales order on the OIF of the custom transaction and create a click-able link to navigate with one click from the OIF of your custom transaction to the OIF of your sales order.
Hope this helps. Let me know if you have any questions.
Best regards,
Georg