BGP announcements and small providers

We service hundreds of dedicated customers and some customers don't mind
renumbering (if they are small) but most of our larger customers who have
more than 100-200 hosts on their network have expressed GREAT opposition to
any such notion of renumbering. Its not that they don't want to do it
because they are lazy, on the contrary, many companies cannot the afford the
downtime or cost asociated with renumbering their LAN/WAN. I agree that
renumbering is an important aspect of address grooming for better agregation
but there are some real $$$ costs to some end-user networks to do so. Also,
how many times can you ask a customer to renumber before they bail and go