In an ACH CTX payment - how to include Customer ID?

Background:  We are making ACH payments using the R04572T2 Create A/P Bank Tape - CTX Format UBE.  We have no mods to the UBE and all is working fine so far.  We have about 10 suppliers live with ACH payments and expect to get up to 300 - 400 eventually.

The problem:  Now we have a large supplier that is requesting we include their customer ID (a 14 char string), in the ACH payment transaction,.  The supplier provided 2 options - see it is "possible" to comply, but I don't like the compromises we need to make.  I am reaching out for suggestions.