How to update Alternate vendor invoices in VendOpenTrans form (Vendor payment - settle transactions )

My requirement is to assign an alternate vendor for each vendor.

so far i have created an alternate vendor field in ledgerjournaltrans, vendtrans , vendtable and vendtransopen ,

now if i post an invoice i can see the alternate vendor for that invoice in vendtrans and ledgerjournaltrans,

if user selects alternate vendor in vendor payment form then click settle transactions it should also list me the main vendor open invoices with alternate vendor.

please help me in achieving this.