"ImageGraph.get" png chart for 1 or more specific goals

I would like to generate a png chart image using ImageGraph (as explained here: http://piwik.org/docs/analytics-api/reference/#ImageGraph) showing the nb_conversions (number of goal conversions) on a monthly basis or so over the last year or so.

The problem is: I have 4 goals in total and would either (preferably) have all the nb_conversions of these goals in one evolution chart (4 lines and maybe a legend) or have a separate chart for all of these goals (i.e. 4 distinct charts in total then).

What I do not know is how to pass idGoal=[1…4] to the ImageGraph method. What I have is
but I do not want to have the nb_conversions of all goals summed up but would like to choose the specific goal by using idGoal parameter of Goals.get (see http://piwik.org/docs/analytics-api/reference/#Goals)

Is this somewhat possible?

not possible (yet?) to plot 4 goals at once, but possible to plot conversions of only 1 goal eg. http://demo.piwik.org/index.php?module=API&method=ImageGraph.get&idSite=7&apiModule=Goals&apiAction=get&token_auth=anonymous&graphType=evolution&period=day&date=previous30&width=500&height=250&idGoal=1