Limited to creating 5 clients within 30 minutes?

I've got a capture page application that I want to integrate with CM via the API, but I keep getting an error telling me I am limited to creating 5 clients within 30 minutes.  This is a potential show-stopper for us, as our traffic patterns sometimes have a number of people joining quickly (say 15 - 30 in an hour) and then long stretches of nobody joining.
Is there a way to work around the 5 clients per 30 minute limitation using the API?  Other than setting up some kind of client creation throttling on our end (not an option for us), how are other Campaign Monitor customers mitigating the issue?

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