We've used sequencing to correctly set Sales Order numbers to the format we'd like to use. Now, we'd like to have generated Invoices use the originating Sales Order numbers as part of their sequence. 

I know this is not the ideal circumstance, but it would be nice to know at a glance which SO an Invoice is tied to. Ideally, the Invoice Number would include a suffix similar to "-1" increasing sequentially for additional invoices.

For example:

SO25001

generates Invoices: 25001-1, -2, etc.

How can this be accomplished?