First I would have simply said that I never made one like that before and I'm afraid I would do a really poor job. If that didn't get rid of them I would say , OK , I'll try but the extra time I will need to design it will mean it costs 3 times as much. If that didn't get rid of them I'd make them a really crappy cake and get paid 3X for it!
Honestly , I think the baker should be able to just say no.