Making Prorate checkbox default to Yes for all Invoices

Summary:

Our client needs the Prorate checkbox to be enabled for all invoices, irrespective of their source and PO matched/non-po matched status.

Content (required):

It should be enabled by default for all invoices so that the freight line amount is allocated to all item lines. Oracle SR has responded that this is not possible by standard feature, hence looking for ideas for a workaround if this can be achieved via a page composer sandbox expression or something?

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