Hook to know about transient window size change?

Hi,

Is there any way to get a hook that will be called on transient size
change?  I am setting initial positions of the transients in
clientwin_mapped_hook, but way too many of them immediately resize
themselves after showing up.

At the moment I use an ugly timer hack:

function position_windows()
    ioncore.clientwin_i(function(i)
        if obj_typename(i:manager()) == "WFrame" then
            ioncore.defer(function()
                set_position(i)
            end)
        end
        return true
    end)
    pos_timer:set(1000, position_windows)
end

Thanks,

-- Sasha