What is the best way to manage a large list of IPs for the MyNetworks variable?

I have a list of IPs that is over 6000 characters long (include or exclude list is equally as long even using CIDR notation), which is beyond what zmprov can handle by the looks of it.

Code:
ERROR: account.INVALID_ATTR_VALUE (zimbramtamynetworks value length(6792) larger then max allowed: 1024)
What would your suggestions be as Zimbra overwrites my main.cf when I restart Postfix?

Thanks,

Craig