Delegating from a /24 network

[Hostmaster]

We have a customer that is asking for 32 IP Addresses; and they will
initially use about 28 of them.

Currently our upstream provider is delegating everything to us, forward and
inverse.

We currently have all fowards in one zone file and all the inverse in
another.

In order for us to delegate this to them, without having to go through arin,
how would someone suggest we modify our zone file?

Something like :

zone abc.com-65.197.3-24 {
    ...
    ...
    ...
}

????

Any suggestions would be appreciated.

They are also wanting to maintain their own dns including inverse.

Douglas