Those options do not appear to be supported. I have both the SplunkJS code for versions 1.1 and 1.4, and those properties are not present. I think they were supported in the old FlashCharts or AdvancedXML components, but those are deprecated.
You are probably correct. The highcharts/svg stuff is not really friendly to such hacks in my experience. You could try to work something out to dig into the CSS hierarchy and set some kind of width parameter, but that would be pretty brittle.