Hi, i've been thinking of creating my own add-on that does pretty much what you did. Since you did the hard part i condensed it a bit to my needs. please find the code below if you are interested:

only additional step is: make a macro that has: /script EMonitor.settarget()

bind this macro to a key and voila ondemand updates.

main "updates" from my side are: playernr = GetNumGroupmates() and ignore dead players (annoying if you keep targetting dead players in scenario's)

thanks for your efforts. feel free to use or ignore any of this.

-- Proof of concept for an Emergency Monitor mod
-- Written by Khalid on the warhammer alliance forums and WoW Temporary Insanity on Kilrogg
-- 9/10/2008
-- Uses some LibSlash from Aiiane and the prettyprint command from http://www.thewarwiki.com/wiki/WAR_API
-- Props to Aiiane, the most helpful person on the Warhammer Alliance forums

-- Plans:
-- Try and make a button that the user can click to turn mod off instead of the slash command
-- More intelligent target picking
-- Extend to Warparty

EMonitor = {}

GroupData = GetGroupData()
LowestName = GameData.Player.name

function EMonitor.Initialize()
    
    -- Register events, list of events gotten from CleanUnitFrames by Aiiane, email=aiiane@aiiane.net
    -- Possibly do not need all these atm
    RegisterEventHandler( SystemData.Events.GROUP_UPDATED "EMonitor.OnGroupUpdated";)
    RegisterEventHandler( SystemData.Events.GROUP_STATUS_UPDATED "EMonitor.OnGroupUpdated";)
    RegisterEventHandler( SystemData.Events.GROUP_EFFECTS_UPDATED "EMonitor.OnGroupUpdated";)
    RegisterEventHandler( SystemData.Events.GROUP_PLAYER_ADDED "EMonitor.OnGroupUpdated";)
    --RegisterEventHandler( SystemData.Events.SCENARIO_BEGIN "EMonitor.OnGroupUpdated";)
    --RegisterEventHandler( SystemData.Events.SCENARIO_END "EMonitor.OnGroupUpdated";)
    RegisterEventHandler( SystemData.Events.SCENARIO_GROUP_JOIN "EMonitor.OnGroupUpdated";)
    RegisterEventHandler( SystemData.Events.SCENARIO_GROUP_LEAVE "EMonitor.OnGroupUpdated";)
    RegisterEventHandler( SystemData.Events.PLAYER_CUR_HIT_POINTS_UPDATED "EMonitor.OnGroupUpdated";)
    --RegisterEventHandler( SystemData.Events.PLAYER_MAX_HIT_POINTS_UPDATED "EMonitor.OnGroupUpdated";)
    RegisterEventHandler( SystemData.Events.PLAYER_EFFECTS_UPDATED "EMonitor.OnGroupUpdated";)
    --RegisterEventHandler( SystemData.Events.PLAYER_DEATH "EMonitor.OnGroupUpdated";)
    RegisterEventHandler( SystemData.Events.PLAYER_DEATH_CLEARED "EMonitor.OnGroupUpdated";)
    
    -- Register a slash command for toggling the mod on and off
    --local success = LibSlash.RegisterSlashCmd("emt";, function() EMonitor_Toggle() end)
    -- pprint("Registering emt, result was=",success)
    -- Turn the mod off, then toggle it on
    --EMonitor_Enabled = false
    --EMonitor_Toggle()

end

-- Checks if the group member is valid, gotten from CleanUnitFrames by Aiiane, email=aiiane@aiiane.net
function EMonitor.IsMemberValid(index)
    return ( GroupData ~= nil and
             GroupData[index] ~= nil and
             GroupData[index].name ~= nil and
             GroupData[index].name ~= L"" )
end

function EMonitor.OnGroupUpdated()

    -- Default lowest health percent as the player
    LowestHealthPercent = (GameData.Player.hitPoints.current * 100)/ GameData.Player.hitPoints.maximum
    
    -- pprint("Player=",LowestHealthPercent)
    
    LowestName = GameData.Player.name
    
    GroupData = GetGroupData()
    playernr = GetNumGroupmates()
    -- Find lowest health percentage and store it
    for i = 1, playernr do
        -- make sure group member is valid
        -- pprint("EMonitor.IsMemberValid=",EMonitor.IsMemberValid(i))
        if (EMonitor.IsMemberValid(i) == true) then
            -- pprint("GroupMember ",i," ",GroupData[i].healthPercent)
            -- Is it lower than the lowest so far?
            if (GroupData[i].healthPercent > 0 ) then
                if (GroupData[i].healthPercent <= LowestHealthPercent ) then
                    -- Save it then
                    LowestHealthPercent = GroupData[i].healthPercent
                    LowestName = GroupData[i].name
                end
            end
        end
    end
    
    -- Now target this lowest health member
    --local success = TargetPlayer(LowestName)
    --DEBUG( L"EMonitor.OnGroupUpdated():Error, Could not target the player with the lowest health, who was")
end

function EMonitor.settarget()
    local success = TargetPlayer(LowestName)
end