How to control the order of different export options for different client formats?

[James Pearson <james-p@moving-picture.com>]

I'm using CentOS 5.x (nfs-utils based on v1.0.9) - and have been using 
the following in /etc/exports:

/export *(rw,async) @backup(rw,no_root_squash,async)

which works fine - hosts in the backup NIS netgroup mount the file 
system with no_root_squash and other clients with root_squash

However, I now want to restrict the export to all clients in a single 
subnet - so I now have /etc/exports as:

/export 172.16.0.0/20(rw,async) @backup(rw,no_root_squash,async)

Unfortunately, hosts in the backup NIS netgroup (which are also in the 
172.16.0.0/20 subnet) no longer mount with no_root_squash

It appears that the subnet export takes precedence over the netgroup 
export (it doesn't matter in what order the subnets/netgroups exports 
are listed in /etc/exports) - so the netgroup client options are ignored 
as a match has already been found in the subnet export.

Is there any way to control the order in which clients are checked for 
export options?

i.e. I would like netgroups to take precedence over subnets

Thanks

James Pearson