MySQL User with Host set to a Range of IP Addresses

I have a hosted MySQL DB that I need to give access to from my customers site. They have a fast broadband connection which can present them with a range of IP addresses from a fixed pool. So I need to lock down the access to their MySQL user so that the Host setting is a range of addresses within a class. Not the whole class. I realise I can use a wildcard such as 81.91.71.% but that is too generous. Their range is more like 81.10.20.1 --> 81.10.20.15 Is there a way to do this other than create 15 users, one for each individual IP address? thanks Mark