It should already work this way. Look in /usr/share/cluster/service.sh,
there is a block of XML data that defines the service resource agent.
Twords the end of the block of XML is a "special" tag this defines the
child node types for that agent. You'll notice each of the child nodes
has a start and stop number. These define the order that the given
children are started and stopped You'll see filesystems are started at
level 2, and ip addresses are started at 3. Since a nfs export is
defined as a child of a fs agent, the nfs exports are turned on after
mounting the filesystem, and before the IP address is active.