Form Personalization: How to validate multiple records?

I would like to use form personalization on the AP payment workbench form

When users select multiple invoices, I have a requirement to validate the remit to supplier fields on the selected invoices and if they do not match, I want to display a warning message

Example: on ADJ_INV_PAY

invoice 1 - remit to supplier name = ABC

invoice 2 - remit to supplier name = DEF

invoice 3 - remit to supplier name = GHI

I want to compare remit to against invoice 1 and 2  (IF ABC != DEF, then display a warning message)

Please advise how this can be done on R12 form

I dont want to use custom.pll