Submitting this for community use. It's a TrafficScript - pretty ugly and in a very early stage but it does what I need it to do and others might find it useful 
Big thanks to Riverbed Support for helping me get the REST API enabled as I spent ages trying to figure out why that wasn't working only to discover it was a menu option (doh!).
The requirement was pretty specific, we're dealing with an application which can handle a failover to a secondary node, but can't handle failing back. So we're not using the Stingray as a load balancer in this case, more as a clever failover utility. The client didn't want the Stingray failing back to the primary node/pool once it was fixed and the Stingray doesn't support no-failback as a default option so we had to revert to a TrafficScript to do what we wanted. Hopefully the code is pretty clear, but if there are any questions or indeed suggestions on how to improve it further let me know!
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# Script Name: killSwitch
# Author: Johnathan Williamson
# Version: 0.1 Alpha
# Disclaimer: Not recommended for production use, YMMV !
# Description This rule disables the primary pools node on initial failure.
#
# The rule runs on every page load.
#
# It uses the subroutines in the stmrestclient rule
################################################################################
import stmrestclient;
## First we pull the current state of each pool. This helps us determine what to do next.
$ActivePool = pool.checknode("ActivePool","192.168.60.11",80);
$SecondaryPool = pool.checknode("SecondaryPool","192.168.60.12",80);
$accept = "application/json";
$resource = "pools/ActivePool";
# If a pool is dead, it indicates all nodes inside it have stopped responding
if ($ActivePool == "DEAD") {
# Get current pool config and set node to disabled
$response = stmrestclient.stmRestGet($resource, $accept);
if ($response["rc"] == 1) {
$poolConfig = $response["data"];
$poolConfig["properties"]["basic"]["disabled"] = ["192.168.60.11:80"];
# The following line results in a few moans in the logs about missing node config, but also means no double node entries in the GUI
#$poolConfig["properties"]["basic"]["nodes"] = [];
}
# Now we've got our disabled node in the poolConfig ... submit it for action
$response = stmrestclient.stmRestPut($resource, $accept, $poolConfig);
if ($response["rc"] == 0) {
log.warn ("CUSTOM TRAFFIC SCRIPT FAILURE - : " . lang.dump($poolConfig));
}
} else if ( $ActivePool == "DISABLED" ) {
# Secondary failover kicks in automatically
}
## Some debug stuff
#log.warn("Primary pool is " . $ActivePool);
#log.warn("Secondary pool is " . $SecondaryPool$);
#log.info ("disabled nodes are " . lang.dump($poolConfig["properties"]["basic"]["disabled"]));
#log.info ("active nodes are " . lang.dump($poolConfig["properties"]["basic"]["nodes"]));
#log.info ("full hash looks like: " . lang.dump($poolConfig));
