Until QB comes up with this feature, as a workaround I am thinking, on the invoice under product section, type the required message/bank details on the empty line. Then save each invoice as recurring invoice. Do this for as many unique messages required.

One thing though, the reports will look capture these descriptions with 0.00 value.

It's not the best way. Ability to have unique custom message for each invoice template would still be the right way to go. Also, QBO does not let standard users select invoice template when printing invoices - only admin can do this. This means they would have to shout out to admin every time they need to generate an invoice using different layout. This is silly.