I feel your pain. It is tempting to tell the buggers to piss off for that CI faux pas... but

You could use a Xantech IRS232a - They work great, aren't too hard to set up an use (as long as you know the C3X RS232 control table) and you can set it up once and re use it for future installs too. You probably should budget (or charge your customer) an additional $500-600 (+ programming) for this though.